#include <stdio.h>

int main(void) {
  int arr[4];
  for (int i = 0; i < 4; i++) scanf("%d", &arr[i]);

  while (arr[0] > 0 && arr[2] > 0) {
    arr[2] -= arr[1];
    if (arr[2] <= 0) {
      printf("Yes\n");
      return 0;
    }
    arr[0] -= arr[3];
    if (arr[0] <= 0) {
      printf("No\n");
      return 0;
    }
  }

  return 0;
}
