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 Rust (1.15.1) (judge verdict: Accepted)

use std::io::Read;

fn digit_sum(v: i32) -> i32 {
    let mut val = v;
    let mut res = 0;
    while val > 0 {
        res += val % 10;
        val /= 10;
    }
    res
}

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).ok();
    let n = buf.trim().parse::<i32>().unwrap();
    let mut res = 10000000;
    for i in 1..n {
        res = std::cmp::min(res, digit_sum(i) + digit_sum(n-i));
    }
    println!("{}", res);
}