#include <iostream>
#include <cstdlib>

using namespace std;

int main()
{
    int n;
    while (cin >> n)
    {
        int* vals = (int*)malloc(n * sizeof(int));
	for (int i = 0; i < n; i++)
	{
	    cin >> vals[i];
	}
	if (n == 1)
	{
	    cout << 1 << endl;
	    continue;
	}
	int diff = vals[n - 1] - vals[n - 2];
	int ind = n - 2;
	while (ind != -1 && vals[ind + 1] - vals[ind] == diff)
	{
	    ind--;
	}
	cout << ind + 2 << endl;
    }
    return 0;
}