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)

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn calc_digit_sum(mut a: usize) -> usize {
    let mut ans = 0;
    while a > 0 {
        ans += a % 10;
        a /= 10;
    }
    ans
}

fn main() {
    let n: usize = read();
    let mut ans = (1..n)
        .map(|i| calc_digit_sum(i) + calc_digit_sum(n - i))
        .min()
        .unwrap();
    println!("{}", ans);
}