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>

int main(void){
    char S[4] = {};
    scanf("%s",S);
    if(S[0]==S[1]&&S[2]==S[3]&&S[0]!=S[3]){
        printf("Yes");
        return 0;
    }else if(S[0]==S[2]&&S[1]==S[3]&&S[0]!=S[3]){
        printf("Yes");
        return 0;
    }else if(S[0]==S[3]&&S[1]==S[2]&&S[0]!=S[1]){
        printf("Yes");
        return 0;
    }
    printf("No");
    return 0;
}