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 <stdlib.h>
#include<iostream>
#include<bits/stdc++.h>
#include<cmath>
#define ll long long
const ll INF=0x3f3f3f3f;
#define mod 109
using namespace std;
//priority_queue
const ll Maxn=1e5;
ll gcd(ll a,ll b)
{
    return b==0?a:gcd(b,a%b);
}
ll kc(ll a,ll b)
{
    ll c=1;
    while(b)
    {
        if(b&1)c=(c*a)%mod;
        a=(a*a)%mod;
        b>>=1;
    }
    return c;
}
bool cmp(double x,double y)
{
    return x>y;
}

int main()
{ ios::sync_with_stdio(false);

 string s;
 cin>>s;
 char ss[103];
 int sum=0;
 for(int i=0;i<=3;i++)
 {
     ss[s[i]-'A']++;
     if(ss[s[i]-'A']==2)sum++,ss[s[i]-'A']-=2;
 }
 if(sum==2)cout<<"Yes\n";
 else cout<<"No\n";
}