#include <stdio.h>

int n;
int seq[10000];

int main(){
	while(scanf("%d", &n)>=0){
		for(int i=0;i<n;i++){
			scanf("%d", seq+i);
		}
		if (n==1) {
			printf("1\n");
			continue;
		}
		int dif = seq[n-1]-seq[n-2];
		int i;
		for(i=n-1;i>0;i--){
			if (seq[i]-seq[i-1] != dif) break; 
		}
		printf("%d\n", i+1);
	}
}