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(){
    char st[5];
    scanf("%s",st);
    int i;
    char tmp[2];
    tmp[0] = st[0];
    int a = 1,b = 0;
    for(i = 1;i<5;i++){
        if(st[i] == tmp[0]) a++;
        else if(b == 0){
            tmp[1] = st[i];
            b++;
        }else if(st[i] == tmp[1]) b++;
    }
    if(a == 2 && b==2) printf("Yes");
    else printf("No");
    return 0;
}