#include<bits/stdc++.h>
using namespace std;
int main(){
  string s;
  cin>>s;
  sort(s.begin(),s.end());
  if(s[0]==s[1]&&s[2]==s[3]&&s[1]!=s[2]){
    cout<<"Yes"<<endl;
  }
  else{
    cout<<"No"<<endl;
  }
  return(0);
}
