#include <stdio.h>
int main() {
  int a, b, c, d, T, A;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  T = (a + d - 1) / d;
  A = (c + b - 1) / b;
  if (T >= A) {
    printf("Yes");
  } else {
    printf("No");
  }

  return 0;
}
