Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in Rust (1.42.0) (judge verdict: Accepted)

use proconio::marker::Chars;
use proconio::{fastout, input};
use std::collections::HashMap;

#[fastout]
fn main() {
    input! {s: Chars};

    let mut map = HashMap::new();

    for i in s.iter() {
        let count = map.entry(i).or_insert(0);
        *count += 1;
    }

    let mut flag = true;

    for (_, value) in map {
        if value != 2 {
            flag = false;
            break;
        }
    }

    if flag && s.len() == 4 {
        println!("Yes")
    } else {
        println!("No")
    }
}