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 C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>

int main() {

    char s[4];
    scanf("%s", s);

    if ((s[0] == s[1]) && (s[0] == s[2]) && (s[0] == s[3])) {
        puts("No");
    } else if ((s[0] == s[1]) && (s[2] == s[3])) {
        puts("Yes");
    } else if ((s[0] == s[2]) && (s[1] == s[3])) {
        puts("Yes");
    } else if ((s[0] == s[3]) && (s[1] == s[2])) {
        puts("Yes");
    } else {
        puts("No");
    }


    return 0;

}