#include <iostream>
using namespace std;
int xs[100003];

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