#include <vector>
#include <iostream>

using namespace std;

int main()
{
	ios_base::sync_with_stdio(false);

	int num;

	while (cin >> num) {
		vector<int> vals;
		vals.reserve(num);

		for (int i = 0; i < num; ++i) {
			int tmp;
			cin >> tmp;
			vals.push_back(tmp);
		}

		if (num < 3) {
			cout << '1' << endl;
			continue;
		}

		int last_i = vals.size() - 1;
		int prev_last_i = last_i - 1;
		int diff = vals[last_i] - vals[prev_last_i];
		int i = prev_last_i;

		while (i >= 0) {
			if (i == 0) {
				cout << i +1  << endl;
				break;
			}
			else {
				int tmp_diff = vals[i] - vals[i - 1];
				if (tmp_diff != diff) {
					cout << i + 1 << endl;
					break;
				}
				--i;
			}
		}

	}

	return 0;
}