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"
	"strings"
)

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

	strs := strings.Split(a, "")
	var x string
	count := 0
	x = strs[0]
	for i := 1; i < len(strs); i++ {
		if x != strs[i] {
			count++
		}
	}

	if count == 1 {
		fmt.Println("Yes")
	} else {
		fmt.Println("No")
	}
}