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 <bits/stdc++.h>

using namespace std;

#define ll long long int

#define REP(i, n) for(int i = 0; i < (n); i++)
#define SREP(i, s) for(int i = 0; i < (s.size()); i++)
#define SORT(v, n) sort(v, v+n);
#define GSORT(v, n) sort(v, v+n, greater<int>());
#define VSORT(v) sort(v.begin(),v.end());
#define VGSORT(v) sort(v.begin(),v.end(),greater<int>());
#define REV(a) reverse(begin(a),end(a));

ll gcd(ll x, ll y){
	if(x<y) swap(x,y);
	if(y==0) return x;
	return gcd(y,x%y);
}

ll lcm(ll x, ll y){
	return (x*y/gcd(x,y));
}

int main(){
	ios::sync_with_stdio(false);cin.tie(0);
//////////////////////////////////////////////
	string s;
	cin >> s;
	bool b=false;
	if(s[0]==s[3]&&s[1]==s[2]) b=true;
	if(s[0]==s[1]&&s[3]==s[2]) b=true;
	cout << (b ? "Yes" : "No") << endl;
//////////////////////////////////////////////
}