#include <iostream>
using namespace std;
unsigned int calculateTriangleNum(unsigned int n);
int main(){
  unsigned int n;
  
  
  cin >> n;
  
  cout  <<  calculateTriangleNum(n) << endl;
  
  return 0;
}
unsigned int calculateTriangleNum(unsigned int n) {
    
    if(n==0)
    {
        return 0;
    }
    else if(n==1)
    {
        return 1;
    }
    else
    {
        return (n % 10 + calculateTriangleNum(n / 10));
    }
}