#include<stdio.h>

int main(void){
	int n,a[131072],i,p;
	scanf("%d",&n);
	for(i = 1;i <= n;i++){scanf("%d",&a[i]);}
	p = n;
	for(i = n;i >= 1;i--){
		if(p == a[i]){p--;}
	}
	printf("%d\n",p);
	return 0;
}