#include <stdio.h>

int main() {
  int a, b, c, d;

  scanf("%d %d %d %d", &a, &b, &c, &d);

  while (a > 0 && c > 0) {
    c = c - b;
    if (c > 0) a = a - d;
  }

  if (c <= 0)
    printf("Yes\n");
  else
    printf("No\n");

  return 0;
}