#include <bits/stdc++.h>
using namespace std;
int sum(int n){
   if(n < 10)  return n;
   return sum(n/10) + n%10;
}
int main(){
    long long N;cin>>N;
    int A=sum(N);
    int B=sum(A);
    int C=sum(B);
    int D=sum(C);
  cout<<D<<endl;
}