Problem:
Score : 200 points

Problem Statement

Takahashi has two positive integers A and B.

It is known that A plus B equals N.
Find the minimum possible value of "the sum of the digits of A" plus "the sum of the digits of B" (in base 10).

Constraints

2 ≤ N ≤ 10^5

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the minimum possible value of "the sum of the digits of A" plus "the sum of the digits of B".

Sample Input 1

15

Sample Output 1

6

When A=2 and B=13, the sums of their digits are 2 and 4, which minimizes the value in question.

Sample Input 2

100000

Sample Output 2

10

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>

int digit_sum(int);

int main(){
  int N;
  scanf("%d", &N);

  int A, B;
  int cnt=100;

  for(int i=1; i<=N/2; i++){
    A=i;
    B=N-i;
    int S=digit_sum(A)+digit_sum(B);
    // printf("(%d %d) S=%d\n", A, B, S);
    if(cnt>S) cnt=S;
  }

  printf("%d\n", cnt);

  return 0;
}

int digit_sum(int N){
  int num=N;
  int sum=0;
  
  for(int i=0; i<10; i++){
    sum+=num%10;
    num/=10;
    if(num==0) break;
  }

  return sum;
}