#include<stdio.h>
int main(){
  int unused __attribute__((unused));
  int A, B, C, D;
  unused = scanf("%d %d %d %d", &A ,&B, &C, &D);

  while(A>0 && C>0){
    C = C-B;
    A = A-D;
  }
  if(C<=0) printf("Yes");
  else if(A<=0) printf("No");
  else if(C<=0 && A<=0) printf("Yes"); 
  return 0;
}