#include <bits/stdc++.h>
using namespace std;
int main() {
  int A,B,C,D;
  cin >> A >> B >> C >> D;
  while(0<=A&&0<=C) {
    //cout << "ぬーん" << endl;
    C-=B;
    if(C<=0) {
      cout << "Yes" << endl;
      return 0;
    }
    A-=D;
    if(A<=0) {
      cout << "No" << endl;
      return 0;
    }
  }
}
