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 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <stdio.h>
#include <vector>
#include <algorithm>
#include <cmath>
#define rep(i,cc,n) for(int i=cc;i<=n;++i)
#define drep(i,cc,n) for(int i=cc;i>=n;--i)
typedef long long ll;
using namespace std;
int main(){
    string s;
    cin>>s;
    int cnt = 0;
    bool flag = true;
    rep(i,0,3){
        cnt = 0;
        rep(j,0,3){
            if(s[i]==s[j]) cnt++;
        }
        if(cnt!=2) flag = false;
    }
    if(flag) cout<<"Yes"<<endl;
    else cout<<"No"<<endl;
    return 0;
}