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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <cstdio>
// #include <iostream>
using namespace std;

int main(int argc, char const *argv[])
{
    char chs[4];
    bool flgs0 = false;
    for (int i = 0; i < 4; i++)
    {
        scanf(" %c", &chs[i]);
    }
    if (chs[0] == chs[1] && chs[2] == chs[3])
    {
        puts("YES");
        return 0;
    }
    if (chs[0] == chs[2] && chs[1] == chs[3])
    {
        puts("YES");
        return 0;
    }
    if (chs[0] == chs[3] && chs[1] == chs[2])
    {
        puts("YES");
        return 0;
    }

    puts("NO");
    return 0;
}