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

int A,B,C,D;

signed main() {
  cin >> A >> B >> C >> D;
  
  while(true) {
    C-=B;
    if(C<=0) {
      puts("Yes");
      return 0;
    }
    A-=D;
    if(A<=0) {
      puts("No");
      return 0;
    }
  }
}
