find your present

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <set>
#include <iostream>

using namespace std;

int main( )
{
    set<int>q;
    int N,i,t;
    while (scanf("%d",&N), N)
    { 
         q.clear( );
        for (i = 0; i < N; i++)
        {
            scanf("%d",&t);
            if(!q.insert(t).second)
                q.erase(t);
        }
        for(set<int>::iterator iter = q.begin(); iter != q.end( ); iter++)
            printf("%d\n",*iter);
    }
                
        return 0;
}