#include <bits/stdc++.h>
#include <cstdlib>

using namespace std;

int main(int argc, char** argv) {
    ios::sync_with_stdio(false);
    int len, start, i, now, prev, dif_now, dif_prev;
    while (cin >> len){
        cin >> prev;
        dif_prev = 0;
        start = 1;
        for (i = 1; i < len; i++){
            cin >> now;
            dif_now = now - prev;
            if (dif_prev != dif_now){
                start = i;
                dif_prev = dif_now;
            }
            prev = now;
        }
        cout << start << endl;
    }
    return 0;
}