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: Accepted)

package main

import (
	"fmt"
	"strings"
)

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

	sliceS := strings.Split(s, "")
	m := make(map[string]int)
	for _, val := range sliceS {
		m[val]++
	}

	flag := 0
	if len(m) == 2 {
		for _, val := range m {
			if val != 2 {
				flag = 1
			}
		}

		if flag == 0 {
			fmt.Println("Yes")
		}
	} else {
		fmt.Println("No")
	}
}