#include <stdio.h>

int main(){
  int a;
  int b;
  int c;
  int d;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  while(b> 0 && d>0){
    c -= b;
    a -= d;
  }
  if(c > d){
    printf("No");
  }
  else{
    printf("Yes");
  }