Shared code

/* 777 */
#include "bits/stdc++.h"
using namespace std;

#define ll long long 

// const int MOD=1e9+7;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	ll n;cin>>n;
	vector<int>vec(n-1);
	for(auto &x:vec)cin>>x;
	int missing_num=0;
	for(int i=1;i<=n;++i)missing_num^=vec[i-1]^i;
	cout<<missing_num;
}