#include<bits/stdc++.h>
using namespace std;


int main(){
    int n;
    cin>>n;
    string s = to_string(n);
    while(s.size()!=1){
        int p = 0;
        for(auto it:s){
            p+=(it-'0');   
        }
        s = to_string(p);
    }   
    cout<<stoi(s)<<endl;
}