#include<stdio.h>

int main(void){
  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){
      printf("Yes");
      break;
    }else{}
    A = A - D;
    if (A <= 0){
      printf("No");
      break;
    }else{}
  }
  return 0;
}
