//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int main(){
  string S; cin >> S;
  int s = (int)S.size();
  
  while(s != 1){
    int T = 0;
    for(int i = 0; i < s; i++){
      T += S[i]-'0';
    }
    
    S = to_string(T);
    s = (int)S.size();
  }
  
  printl(S);
  
  return 0;
}