#import <Foundation/Foundation.h>

int main() {
  NSInteger A, B, C, D;
  scanf("%ld %ld %ld %ld", &A, &B, &C, &D);
  NSInteger takahashi = ceil(A / D);
  NSInteger aoki = ceil(C / B);
  printf("%s\n", takahashi <= aoki ? "Yes" : "No");
  return 0;
}