#include <stdio.h>

int main() {

	int n;

	while (scanf("%d",&n) > 0) {
		
		int i;
		long array[n];

		for (i = 0; i < n; i++) {
			scanf("%ld",&array[i]);
		}

		i = n-1;
		long diff = array[i] - array[i-1];

		i = i-2;

		while(1){
			long newDiff = array[i+1] - array[i];
			if (newDiff != diff) break;
			i--;
			if (i == 0) {
				i--;
				break;
			}
		}
		printf("%d\n",i+2);
	}

	return 0;
}