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 ch[100];
    scanf("%[^\n]s",ch);
    if(ch[0] == ch[1] && ch[2]==ch[3] && ch[0]  != ch[2] || ch[0] == ch[2] && ch[1]==ch[3] && ch[0] != ch[1] || ch[0] == ch[3] && ch[1]==ch[2] && ch[0]  != ch[1]) printf("Yes");
    else printf("No");
    return 0;
}