#include <stdio.h>
int main(void){
  int A, B, C, D, e = 0;
  scanf("%d", &A);
  scanf("%d", &B);
  scanf("%d", &C);
  scanf("%d", &D);

  while(A >= 0 && C >= 0){
    C -= B;
    if(C <= 0) e += 1; 
    A -= D;
  }
  if(e == 1) printf("Yes\n");
  else printf("No\n");
} 