#include <iostream>

using namespace std;

int main(void) {
	
	while(true) {
	
		int delka;
		cin >> delka;
		if(cin.eof()) break;
		
		int pole[delka];
		
		for(int i = 0; i < delka; i++) {
			cin >> pole[i];
		}
		
		if(delka == 1) {
			cout << 1 << endl;
			continue;
		}
		
		int index = 1;
		int rozdil = pole[0] - pole[1];
		
		for(int i = 1; i < delka; i++) {
			int r = pole[i - 1] - pole[i];
			if(r != rozdil) {
				rozdil = r;
				index = i;
			}
		}
		
		cout << index << endl;
	
	}
	
	
	
	
}