#import <Foundation/Foundation.h>

int main() {
  NSInteger A, B, C, D;
  scanf("%ld %ld %ld %ld", &A, &B, &C, &D);
  while (A > 0 && C > 0) {
    C -= B;
    if (C <= 0) {
      break;
    }
    A -= D;
  }
  printf("%s", A <= 0 ? "No" : "Yes");
  return 0;
}