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 Go (1.6) (judge verdict: Wrong Answer)

package main

import "fmt"

func main() {
	var s string
	fmt.Scan(&s)

	x := make([]int, 30)
	for _, ss := range s {
		x[ss-'A']++
	}

	flg := true
	for _, xx := range x {
		if !(xx == 0 || xx == 2) {
			flg = false
		}
	}

	if flg {
		fmt.Println("YES")
	} else {
		fmt.Println("NO")
	}
}