#include<bits/stdc++.h>
using namespace std;
int main(){
    map<int,int> m;
    for(int i=1;i<=10;++i)m.emplace(i,0);
    vector<int> b(9);
    for(int i=0;i<9;++i)cin>>b[i];
    for(auto x:b)++m[x];
    int ans;
    for(auto x:m)if(x.second==0)ans=x.first;
    cout<<ans<<endl;
}