#include<bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){
    int a, b,c;
    cin >> a >> b >> c;
    vector<int> num(4);
    num[a]++;num[b]++;num[c]++;
    for(int i = 0;i < 4;++i){
        if(num[i] == 3){
            cout << i << endl;
            return 0;
        }
    }

    bool all_one = true;
    int zero =-1;
    for(int i = 0;i < 4;++i){
        if(num[i] != 1 && num[i] != 0) all_one = false;
        if(num[i] == 0) zero = i;
    }

    if(all_one){
        cout << zero << endl;
        return 0;
    }

    for(int i = 0;i < 4;++i){
        if(num[i] == 1){
            cout << i << endl;
            return 0;
        }
    }

}