#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<algorithm>
#include<vector>
#include<math.h>
#include<stack>
#include <typeinfo>  
using namespace std;
int main(void){
    string a, b, c; cin >> a >> b >> c;
    if(a == b || a == c){
        cout << a << endl;
    }else{
        cout << b << endl;
    }
return 0;
}