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 (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>

int main()
{
    int ca[256] = {};
    int cnt = 0;
    char ch;

    for (int i = 0; i < 4; i++) {
        ch = getchar();

        if (!ca[ch]) {
            cnt++;
            ca[ch] = 1;
        }
    }

    if (cnt == 2) {
        printf("Yes\n");
    }
    else {
        printf("No\n");
    }
    
    return 0;
}