#include <bits/stdc++.h>
#define FastIO ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
using namespace std;
typedef long long ll;
int main() {
    FastIO;
    ll i, j, rs, N;
    cin >> N;
    vector<ll> lucky(N);
    for(i = 0; i < N; i++)
        cin >> lucky[i];
    rs = -1;
    vector<ll> ans(N);
    stack<ll> free_places;
    for(i = 1; i < N; i++) {
        if(lucky[i] == lucky[i - 1])
            continue;
        for(j = 0; j < min(lucky[i] - lucky[i - 1], i - rs); j++)
            ans[i - j] = j + lucky[i - 1];
        while(j < i - rs)
            free_places.push(i - j++);
        while(j < lucky[i] - lucky[i - 1]) {
            if(free_places.empty()) {
                cout << "NEM\n";
                return 0;
            }
            ans[free_places.top()] = j++ + lucky[i - 1];
            free_places.pop();
        }
        rs = i;
    }
    cout << "IGEN\n";
    for(const auto &x : ans)
        cout << x << ' ';
    cout << '\n';
    return 0;
}