#include <stdio.h>

// write the prototype below
int digitSum(int n);


// complete the main function to read input, call functions, and display output
int main(void) {
  int num = 0;
  scanf("%d", &num);
  int result = digitSum(num);
  printf("%d", result);
  return 0;
}

// complete the function below
int digitSum(int n) {
    // base case
  if(n == 0){
    return 0;
  }
    // recursive step
    else {
    return n%10 + digitSum(n / 10);
  }

}