#include <iostream>

using namespace std;

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

    int N = 0;
    long index = 0;
    int first = 0, second = 0;
    int d = 0;
    
    cin >> N;
    
    cin >> first;
    for (int i = 0; i < N - 1; i++) {
        cin >> second;
        int dNext = second - first;
        if (dNext != d) {
            d = dNext;
            index = i;
        }
        first = second;
    }
    
    cout << index + 1 << endl;
    
    return 0;
}