    #include<iostream>
    using namespace std;
    int main() {
    	int A,B,C,D;
        cin >> A>>B>>C>>D;      
      
      	A%C	
      if((A+D-1)/D >= (C+B-1)/B){
      	cout << "Yes" <<endl;
      }
      else{
        cout << "No" << endl;
      }
    }