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: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
typedef long long llong;
const int inf = 1 << 20;
const int mod = 1e9 + 7;

int main() {
   string s;
   cin >> s;
   map<char, int> m;
   rep(i, 4) m[s[i]]++;
   int cnt = 0;
   for (char c = 'A'; c <= 'Z'; c++) {
      if (m[c] == 2)
         cnt++;
   }
   if (cnt == 2)
      cout << "Yes" << endl;
   else
      cout << "No" << endl;

   return 0;
}