#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";
	}
	else
	{
		cout<<"No";
	}
	return 0;
}