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>

int main()
{
    char s[5];
    char a=0,b=0,x;
    int countA=0,countB=0;
    int i,flag=0;

    scanf("%s",s);
    for(i=0;i<4;i++)
    {
        x=s[i];
        if(x==a)countA++;
        else if(x==b)countB++;
        else if(!a)
        {
            a=x; countA++;
        }
        else if(!b)
        {
            b=x; countB++;
        }
        else break;
    }
    if(countA==2&&countB==2)flag=1;
    if(flag)printf("Yes");
    else printf("No");
}