#include <stdio.h>

int main() {

int a, b, c, d;

scanf("%d %d %d %d\n",&a, &b, &c, &d);

while ( 1 ) {
  c = c - b;

  if (c<=0) {
    printf("Yes\n");
    break;
  }

   a = a - d;
   if (a<=0) {
     printf("No\n" );
     break;
   }


}

  return 0;
}
