杭电acm 2095 find your present (2)

#include<iostream>
using namespace std;
int main()
{
    int n,x,y;
    while(cin>>n,n)
    {
         cin>>x;          
         while(--n)
         {
             cin>>y;
             x=x^y;
         }
         cout<<x<<"\n";
    }
    return 0;
}