#include<iostream>
using namespace std;
int main(){
    int n;
    cin>>n;
    if(n<1 || n>10000){
        cout<<"Invalid input";
        return 0;
    }
    int num,result=0;
    for(int i=0;i<n;i++){
        cin>>num;
        if(num<-10000 || mun>10000){
            cout<<"Invalid input";
            return 0;
        }
        result^=num;
    }
    cout<<result;
    return 0;
}