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 (
	"bufio"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)
 
func run() {

	var S string;
    S = next();
	solve(S);

}

func solve(S string){

	if len(strings.Replace(S, S[0:1], "", 2)) == 0 {
		Println("No")
		return
	}

	if len(strings.Replace(strings.Replace(S, S[0:1], "", 2), strings.Replace(S, S[0:1], "", 2)[0:1], "", 2)) == 0 {
		Println("Yes")
	}else {
		Println("No")
	}
}


// --- template ---
// Thanks https://gist.github.com/halllllll/853ab587fd82ee3ffe6f7fb7fb499695
 
var sc = bufio.NewScanner(os.Stdin)
var out = bufio.NewWriter(os.Stdout)
 
// Caution: You will get unexpected result if a single token is larger than this size.
const BufferSize = 64 * 1024 * 1024
 
func Print(a ...interface{}) (n int, err error) {
	return fmt.Fprint(out, a...)
}
 
func Printf(format string, a ...interface{}) (n int, err error) {
	return fmt.Fprintf(out, format, a...)
}
 
func Println(a ...interface{}) (n int, err error) {
	return fmt.Fprintln(out, a...)
}
 
func next() string {
	sc.Scan()
	return sc.Text()
}
 
func nextInt() int {
	a, err := strconv.Atoi(next())
	if err != nil {
		log.Fatal(err)
	}
	return a
}

func nextFloat() float64 {
	a, err := strconv.ParseFloat(next(), 64)
	if err != nil {
		log.Fatal(err)
	}
	return a
}


type IntHeap []int
func (h IntHeap) Len() int           { return len(h) }
func (h IntHeap) Less(i, j int) bool { return h[i] > h[j] }
func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *IntHeap) Push(x interface{}) {
	// Push and Pop use pointer receivers because they modify the slice's length,
	// not just its contents.
	*h = append(*h, x.(int))
}

func (h *IntHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

/////数字と文字
// 基本クラス
type NS struct {
    Num int
    Str string
}

//////　数字と数字
// 基本クラス
type NN struct {
    Num1 int
    Num2 int
}

 
func main() {
	sc.Buffer(make([]byte, 0, BufferSize), BufferSize)
	sc.Split(bufio.ScanWords)
	run()
	out.Flush()
}