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

#define all(a) a.begin(),a.end()

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);
    int n;
    cin>>n;
    vector<int> v(n);
    vector<int> ans(n, -1);
    bool pos=true;
    vector<bool> has(2*n+1, false);
    for (int i=0;i<n;i++){
        cin>>v[i];
        if (i && v[i]<v[i-1]) pos=false;
        if (i && v[i]!=v[i-1]) ans[i]=v[i-1];
        has[v[i]]=true;
    }
    if (!pos){
        cout<<"NEM";
        return 0;
    }
    int cur=0;
    for (int i=0;i<n;i++){
        while (has[cur] && cur<=2*n) cur++;
        if (cur>2*n) cur=2*n;
        if (ans[i]==-1) {
            ans[i]=cur;
            cur++;
        }
    }
    cur=0;
    vector<bool> other(2*n+1,false);
    for (int i=0;i<n;i++){
        other[ans[i]]=true;
        while(other[cur] && cur<=2*n) cur++;
        if (cur!=v[i]) pos=false;
    }
    if (pos){
        cout<<"IGEN\n";
        for (int i : ans) cout<<i<<" ";
    }
    else {
        cout<<"NEM";
    }
}