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)

// -*- coding:utf-8-unix -*-

use proconio::input;
use std::collections::HashMap;

fn main() {
    input! {
        n: String,
    }
    let mut count = HashMap::new();
    for c in n.chars() {
        if count.contains_key(&c) {
            *count.get_mut(&c).unwrap() += 1
        }
        else {
            count.insert(c, 1);
        }
    }
    let mut ans = true;
    for (_k, v) in count {
        if v != 2 {
            ans = false;
            break;
        }
    }
    println!("{}", if ans { "Yes" } else { "No" });
}