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>
#include <string.h>

int main()
{
    char s[5];
    int i;

    scanf( "%s", s );

    if( strlen(s) != 4 ) //文字列の長さ判定
        {
            puts("No");
            return 0;
        }
    

    for (i = 0; i <= 3; i++) //大文字判定
    {
            if (s[0] >= 'A' && s[0] <= 'Z')
                continue;
            else
            {
                puts("No");
                return 0;
            }
    }


    if (s[0] == s[1] )
        {
            if (s[2] == s[3] && s[0] != s[2] )
                puts("Yes");
        }
    else if (s[0] == s[2] )
        {
            if (s[1] == s[3] && s[0] != s[1])
                puts("Yes");
        }
    else if (s[0] == s[3])
        {
            if (s[1] == s[2] && s[0] != s[1] )
                puts("Yes");
        }
    else
            puts("No");

    
    
    return 0;
}