#include <stdio.h>
#include <vector>


using namespace std;

int main(void) {
	
	int n;
	while(scanf("%d", &n) == 1) {
		vector<int> vct(n+1);
		for(int i = 0; i < n ; i ++) {
			int tmp; 
			scanf("%d", &tmp);
			vct[i] = tmp;		
		}
		
		if (n == 1) {
			printf("1\n");
			continue;
		}
		
		if (n == 2) {
			printf("1\n");
			continue;
		}
		
		
		int ix = n - 1;
		int last = vct[n-2] - vct[n - 1];
		for (int i = n -3 ; i >= 0; i--) {
			if (vct[i] - vct[i+1] == last) {
				ix--;
			} else {
			break; 
			}
		}
		
		printf("%d\n", ix); 
	}

	return 0;
}