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

/*
 * 
 */
int main(int argc, char** argv) {

    std::ios::sync_with_stdio(false);
    int a;
    while(cin >> a){
        vector<int> v;
        for(int i = 0; i < a; i++){
            int tmp;
            cin >> tmp;
            v.push_back(tmp);
        }
        int rozdil = 0, res = 0;
        rozdil = v[v.size()-1] - v[v.size()-2];
        for(int j = v.size()-2; j > 0; j-- ){
            if(rozdil != v[j]-v[j-1]){
                res = j;
                break;
            }
        
        }
        cout << res+1 << endl;
    }
    
    return 0;
}