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<stdlib.h>
#include<math.h>

int main()
{
    char S[5];
    int i,j=0;
    scanf("%s",S);
    if(S[1]!=S[0])j++;
    if(S[2]!=S[0]&&S[2]!=S[1])j++;
    if(S[3]!=S[0]&&S[3]!=S[1]&&S[3]!=S[2])j++;

//printf("%d",j);

    if(j==1)printf("Yes");
    else printf("No");
    return 0;
}