#include <bits/stdc++.h>
using namespace std;

int main() {
  int A,B,C,D,a,b,c,d,i;
  cin >> A >> B >> C >> D;
  i = 1;
  while(true){
    C = C - B;
    A = A - D;
    if(C <= 0){
      cout << "Yes" << endl;
      break;
    }
    else if(A <= 0 && C > 0){
      cout << "No" << endl;
      break;
    }
  }
}
