compP chal1 19/12/2019

#include <bits/stdc++.h>
#define newline '\n'
#define uns unsigned
#define ll long long
#define deb(x) clog << x << ' '
#define debnewL(x) clog << x << newline
using namespace std;
///*********************

int main()
{
    int n, ans;
    cin >> n;
    cin >> ans;//x1
    for (int i = 1; i <= n * 2; i++)
    {
        int x;
        cin >> x;
        ans ^= x;
    }

    cout << ans;
    return 0;
}