#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(){
  int A, B, C, D;
  int dta, dtb;
  scanf("%d %d %d %d", &A, &B, &C, &D);

  dta = A / D;
  if(A % D != 0)dta+=1;
  dtb = C / B;
  if(C % B != 0)dtb+=1;


  //printf("ta: %d  tb: %d\n", dta, dtb);
  if(dta >= dtb){
    printf("Yes\n");
  }else{
    printf("No\n");
  }

  return 0;
}