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: Wrong Answer)

#include<stdio.h>
int main()
{
    char a[4],p;
    int i,y=1,e=1;
    scanf("%s",a);
    for(i=1;i<strlen(a);i++){
        if(a[0]==a[i]){
           y++;
        }
        else if(a[1]==a[i]){
            e++;
        }
    }
    if(y==2&&e==2){
        printf("Yes\n");
    }
    else{
        printf("No\n");
    }
    return 0;
}