#include <bits/stdc++.h>
using namespace std;
int main() {
  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;
  }
}