#include<bits/stdc++.h>
using namespace std;
int main() {
    int n; cin >> n;
    vector <int> v;
    for(int i=0; i<n; i++) {
        int e; cin >> e;
        v.push_back(e);
    }
    sort(v.begin(), v.end());
    for(int i=0; i<v.size(); i=i+2) {
        if(v[i]!=v[i+1]) {
            cout << v[i] << endl;
            break;
        }
    }
    return 0;
}