#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <cmath>
#include <array>
#include <string>
#include <cstdio>
#include <iterator>
#include <unordered_set>
#include <cstdint>
#include <queue>
#include <stack>
#include <deque>
#include <numeric>
#include <fstream>
using namespace std;

template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
void dbg_out() { cout << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cout << ' ' << H; dbg_out(T...); }
#ifdef LOCAL
#define dbg(...) cout << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif

/*

notes:

int64_t
stoi(string s) -> string to int
to_string() -> int (or else) to string

vector declaration:
vector<ll> v(n, 0)
vector<vector<ll>> v(n, vector<ll>(n, 0));

{if statement} ? {truth value} : {false value}

set lower bound/upper bound:
 	// . . . m1 . . . d . . . . m2
    auto m1_it = b.lower_bound(d);
    advance(m1_it, -1);
    m1 = *m1_it;
	m2 = *b.upper_bound(d);

#ifdef LOCAL
    freopen("in.txt","r",stdin);
    freopen("out.txt","w",stdout);
#endif

constexpr auto lcm(auto x, auto... xs)
{
	return ((x = std::lcm(x, xs)), ...);
}

std::gcd(int a, int b)

*/

typedef long long ll;

void solve() {

    ll n, m, l, k;
    cin >> n >> m >> l >> k;

    if(k == 0) {
        cout << "YES\n";
        for(ll i = 0; i < n; i++) {
            for(ll j = 0; j < m; j++) {
                cout << "R";
            }
            cout << "\n";
        }
        return;
    }

    if(l % 3 != 0) {
        cout << "NO";
        return;
    }

    ll nmax = n - l + 1;
    ll mmax = m - l + 1;

    //cerr << "\nnmax=" << nmax;
    //cerr << "\nmmax=" << mmax;

    ll lmax = nmax * mmax;
    if(lmax < k) {
        cout << "NO";
        return;
    }

    string f;
    for(ll i = 0; i < m; i++) {
        f += 'F';
    }
    vector<string> v(n, f);

    if(m >= n) {
        ll rem = k;

        map<char, ll> mp;

        for(ll i = 0; i < n; i++) {
            //cerr << "\ni=" << i;
            mp['R'] = rem;
            mp['G'] = rem;
            mp['B'] = rem;
            for(ll j = 0; j < mmax; j++) {
                //cerr << "\nj=" << j;
                //cerr << "\nv=" << v;
                //cerr << "\nmp=" << mp;
                char filletter = 'F';
                if(i % 3 == 0) {
                    filletter = 'R';
                }else if(i % 3 == 1) {
                    filletter = 'G';
                }else{
                    filletter = 'B';
                }
                v[i][j] = filletter;
                mp[filletter]--;
                if(i >= l - 1) {
                    rem--;
                }
                if(j == mmax - 1 || mp[filletter] == 0 || rem == 0) {
                    for(ll fin = j; fin < j + l; fin++) {
                        v[i][fin] = filletter;
                    }
                    break;
                }
                if(rem == 0) {
                    break;
                }
            }
            if(mp['R'] == 0 && mp['G'] == 0 && mp['B'] == 0 || rem == 0) {
                break;
            }
        }

        
        for(ll i = 0; i < n; i++) {
            for(ll j = 0; j < m; j++) {
                if(v[i][j] == 'F') {
                    if(i == 0) {
                        v[i][j] = 'B';
                    }else{
                        v[i][j] = v[i-1][j];
                    }
                }
            }
        } 
         
    }else{
        ll rem = k;

        map<char, ll> mp;

        for(ll j = 0; j < m; j++) {
            //cerr << "\ni=" << i;
            mp['R'] = rem;
            mp['G'] = rem;
            mp['B'] = rem;
            for(ll i = 0; i < nmax; i++) {
                //cerr << "\nj=" << j;
                //cerr << "\nv=" << v;
                //cerr << "\nmp=" << mp;
                char filletter = 'F';
                if(j % 3 == 0) {
                    filletter = 'R';
                }else if(j % 3 == 1) {
                    filletter = 'G';
                }else{
                    filletter = 'B';
                }
                v[i][j] = filletter;
                mp[filletter]--;
                if(j >= l - 1) {
                    rem--;
                }
                if(i == nmax - 1 || mp[filletter] == 0 || rem == 0) {
                    for(ll fin = i; fin < i + l; fin++) {
                        v[fin][j] = filletter;
                    }
                    break;
                }
                if(rem == 0) {
                    break;
                }
            }
            if(mp['R'] == 0 && mp['G'] == 0 && mp['B'] == 0 || rem == 0) {
                break;
            }
        }

        
        for(ll i = 0; i < n; i++) {
            for(ll j = 0; j < m; j++) {
                if(v[i][j] == 'F') {
                    if(j == 0) {
                        v[i][j] = 'B';
                    }else{
                        v[i][j] = v[i][j-1];
                    }
                }
            }
        }
        
    }

    cout << "YES\n";
    for(const auto & s : v) {
        cout << s << "\n";
    }


}

int main()
{
	std::ios_base::sync_with_stdio(false);

	solve();

	return 0;
}