#include <iostream>
#include <algorithm>
using namespace std;
const int N = 100010;
int a[N];
int main(){
int n;
scanf("%d", &n);
for (int i = 1; i < n; i ++) scanf("%d", &a[i]);
sort(a + 1, a + n);
for (int i = 1; i < n; i ++)
if (a[i] != i){
printf("%d\n", i);
return 0;
}
printf("%d\n", n);
return 0;
}