#include <iostream>
#include <vector>


int main() {
	using namespace std;
    std::ios::sync_with_stdio(false);
	int count;
	while (cin >> count) {
	std::vector<size_t> v(count);
	for (int i = 0; i < count; ++i) {
		cin >> v.at(i);	
	}
	if (count == 1) {
		cout << 1 << '\n';
		continue;
	}
	int diff = v.at(count -1) - v.at(count -2);
	bool c = false;
	for (int i = count - 2; i > 0; --i) {
		int newdiff = 0;
		newdiff = v[i] - v[i-1];
		if (newdiff != diff) {
			cout << (i + 1) << '\n';
			c = true;
			break;
		}
	}
	if (!c)
		cout << 1 << '\n';
	}
	
	return 0;
}