#include <stdio.h>

int main()
{
  int a, b;
  int c, d;
  int i = 1;
  
  scanf("%d %d %d %d", &a, &b, &c, &d);
  
  while (i > 0) {
    c = c - b;
    
    if (c <= 0) {
      printf("Yes");
      break;
    }
    
    a = a - d;
    
    if (a <= 0) {
      printf("No");
      break;
    }
  }
    
  return 0;
}