#include <bits/stdc++.h> 
using namespace std;
#include <stdio.h>
#include <iomanip>
#include <iostream>
#include <string>
#include <algorithm>

int main(){
  int a;
  cin >> a;
  while(true){
    string str;
    str = to_string(a);
    int count =0;
    	for(int i=0;i<str.size();i++){
     	 int b = a%10;
     	 a = a/10;
     	 count += b;
    	}
    a = count;
   		 if(a/10==0){
    	  break;
           
  	      }
  }
  cout << a;
}