#include<iostream>
#include<cstring>
using namespace std;
int a[1314520],ans,x;
unsigned n;
int main(){
	cin >> n;
	for (int i=1; i<=n-1; i++){
		cin >> x;
		ans^= x;
		ans^=i;
	}
	ans^=n;
	cout << ans;
	return 0;
}

晚风拂过脸颊~