#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 = 1+ ((A - (A % D)) / D);
  y = 1+ ((C - (C % B)) / B);
  if (x>y) {
    printf("No");
  }
  else {
    printf("Yes");
  }
  return 0;
}
