#include <bits/stdc++.h>
using namespace std;

#define int long long


signed main() {
    int n, m, k;
    cin >> n >> m >> k;

    vector<pair<int, int> > a(m);

    for(int i = 0; i < m; i++) {
        cin >> a[i].first;
        a[i].second = i+1;
    }

    sort(a.begin(), a.end());
    vector<pair<int, int> > ans;

    int index = 0;
    int cnt = 0;
    for(int i = 1; i <= n; i++) {
        while(cnt < k && index<m) {
            if (i <= a[index].first) {
                ans.push_back({a[index].second, i});
                cnt++;
                index++;
            } else {
                index++;
            }
        }
        cnt = 0;

    }


    cout << ans.size() << endl;
    for(auto [x, y] : ans) {
        cout << x << ' ' << y << endl;
    }




}