#include <stdio.h>
 
int main(void) {
  int A, B, C, D, x, y;
  if(scanf("%d %d %d %d", &A, &B, &C, &D)==1);
  x = (A - (A % D)) / D;
  if(A%D!=0) {
    x ++;
  }
  y = (C - (C % B)) / B;
    if(C%B!=0) {
    y ++;
  }
  if (x<y) {
    printf("No");
  }
  else {
    printf("Yes");
  }
  return 0;
}