#include <bits/stdc++.h>
using namespace std;
using G=vector<vector<int>>;
typedef long long ll;
#define rep(i,l,r) for(int i=(l);i<(r);++i)

int main(){
	vector<int> v(4);
	rep(i,0,3){
		int a; cin>>a;
		v[a]++;
	}
	rep(i,0,4){
		if(v[i]==3){cout<<i<<endl; return 0;}
	}
	rep(i,0,4){
		if(v[i]==2){
			rep(j,0,4){
				if(v[j]==1){cout<<j<<endl; return 0;}
			}
		}
	}
	rep(i,0,4){
		if(v[i]==0){cout<<i<<endl; return 0;}
	}
}