#include <stdio.h>
int main(void){
  int A, B, C, D, e = 0;
  scanf("%d", &A);
  scanf("%d", &B);
  scanf("%d", &C);
  scanf("%d", &D);

  while(A >= 0 && B >= 0){
    A -= D;
    if(A <= 0) {
      e += 1;
      break;
    }
    C -= B;
  }
  if(e == 1) printf("No\n");
  else printf("Yes\n");
}