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 int long long
#define double long double
#define rep(i,n) for(int i=0;i<n;i++)
#define mod 1000000007 // 10^9+7
#define INF 99999999999 //10^12-1
#define dev 998244353 //tenka1
#define P pair<int,int>
#define F first
#define S second
char c[4];
signed main(){
    cin>>c[0]>>c[1]>>c[2]>>c[3];
    sort(c,c+4);
    if(c[0]==c[1]&&c[2]==c[3]&&c[1]!=c[2])puts("Yes");
    else puts("No");
    return 0;
}