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 S string
  m := make(map[rune]int)
  fmt.Scan(&S)

  for _, s := range S {
    m[s]++
  }
  
  if len(m) != 2 {
		fmt.Println("No")
  } else {
    for _, v := range m {
      if v != 2 {
        fmt.Println("No")
        return
      }
    }
    fmt.Println("Yes")
  }
}