Sicily 2005. Lovely Number

#include<iostream>
#include<cstring>

using namespace std;

int a[1000000];

int main()
{
    int n;
    while(cin >> n){
        memset(a,0,sizeof(a));
        while(n--){
            int b;
            cin >> b;
            a[b]++;
        }
        for(int i=0; i <= 1000000; i++){
            if(a[i]%2==1) {
                cout << i << endl;
                break;
            }
        }
    }
}