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