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>
#define LENGTH 4

int main(){
    int i,j;
    char S[4];
    int cnt = 0;
    scanf("%s",S);
    for(i=0;i<LENGTH - 1;i++){
        for(j=i+1;j<LENGTH;j++){
            if(S[i]==S[j]) cnt++;
        }
    }
    if(cnt == 2){
        printf("Yes\n");
    }else{
        printf("No\n");
    }
    return 0;
}