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

using namespace std;

#define DEB(x) cout << #x << " = " << x << endl;

int main(void) {
    int n;
    int nums[1000];
    int diffs[1000];
    while (scanf("%d", &n) == 1) {
        for (int i = 0; i < n; i++) {
            scanf("%d", &nums[i]);
            //printf("%d\n", nums[i]);
        }

        for (int i = n - 1; i > 0; i--) {
            diffs[i] = nums[i] - nums[i - 1];
        }

        int maxLen = 0;
        int len = 1;
        int maxNum = 0;
        int diff;

        //for (int i = n - 1; i > 0;) {
        int i = n - 1;
        while (i > 1 && diffs[i] == diffs[i - 1]) {
            i--;
        }
        //DEB(i)
        if (n == 1) i = 1;
        printf("%d\n", i);
        //}
    }

    return 0;
}