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
	fmt.Scan(&S)
	for i := 0; i < 4; i++ {
		c := S[i]
		n := 0
		for j := 0; j < 4; j++ {
			if i == j {
				continue
			}
			if c == S[j] {
				n++
			}
		}
		if n != 1 {
			fmt.Println("No")
			return
		}
	}
	fmt.Println("Yes")
	return
}