#include <bits/stdc++.h>
using namespace std;
 
int a[10000010],n,i,j;
int main(){
    cin>>n;
    for(i = 0;i < n;i++){
        cin>>a[i];
    }
     
    sort(a,a+n);
    int c = 0;
    for(i = 0;i < n;i++){
        c++;
        if(i == n - 1 || a[i] != a[i + 1]){
            if(c % 2 == 1){
                cout<<a[i]<<endl;
                break;
            }
             
            c = 0;
        }
    }
}
/**************************************************************
	Problem: 1472
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:23 ms
	Memory:41140 kb
****************************************************************/