#include <stdio.h>

int main(void) {
	int n, a[100001], num;
	int i, count = 0;
	scanf("%d", &n);
	for(i = 1;i <= n;i++){
		scanf("%d", &a[i]);
	}
	num = n;
	for(i = n;i > 0;i--){
		//printf("%d ", a[i]);
		if(a[i] == num){
			num--;
		}
	}
	printf("%d\n", num);
	
	return 0;
}