#include <bits/stdc++.h> using namespace std; int main() { int a[1010]={0}, n, x,ma = -999999; cin >> n; for (int i = 1; i <= n; i++) { cin >> x; a[x]++; } for (int i = 1000; i >= 0; i--) { if (a[i]%2!=0) { cout<<i; } } return 0; }