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"

func main() {
	var in string
	fmt.Scanf("%s", &in)

	dic := make(map[string]int)
	for _, v := range in {
		dic[string(v)]++
	}

	if len(dic) != 2 {
		fmt.Println("No")
	} else {
		c := true
		for _, v := range dic {
			if v != 2 {
				c = false
			}
		}
		if c {
			fmt.Println("Yes")
		} else {
			fmt.Println("No")
		}
	}

}