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 s[4];
    int i, j = 0, k,l=0;
    scanf("%s",&s);
    for(i=1; i<=3; i++)
    {
        if(s[0] == s[i])
        {
            j = 1;
            k = i;
        }
    }
    if(j == 1)
    {
        if(k == 1)
        {
            if(s[2] == s[3] && s[2] != s[0])
                l = 1;
        }
        else if(k == 2)
        {

            if(s[1] == s[3] && s[1] != s[0])
                l = 1;
        }
        else if(k == 3)
        {

            if(s[1] == s[2] && s[1] != s[0])
                l = 1;
        }

    }
    if(j == 1 && l == 1)
        printf("Yes\n");
    else
        printf("No\n");

    return 0;
}