#include<bits/stdc++.h>
#include <iostream>
#include<assert.h>
using namespace std;
//const int N = 1e5+9;
//char s[N];

int main() {
	// your code goes here
	int n; cin>>n;
	bool watched[n+1];
	for(int i = 1; i<n; i++){
		watched[i] = false; //initially everything is false
	}
	for( int i = 1; i<n; i++){
		int episode; cin>> episode;
		watched [episode]= true;
	}
	int not_watched = -1;
	for(int i = 1; i<n; i++){
		if(!watched[i]){
			not_watched = i;
			
		}
	}
	cout << not_watched << endl;
	assert(not_watched != -1);
	
	return 0;
}