#include<stdio.h>
int main(){
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  while(a > 0 && b > 0){
    a = a - d , c = c - b;}
  if(a <= 0) printf("No\n");
  if(c <= 0) printf("Yes\n");
  return 0;
}