#include<stdio.h>

int battle(int a, int b, int c, int d) {
   while(a > 0 && c > 0) {
      a -= d;
      c -= b;
   }
   if(c > 0) {
      return 0;
   }
   return 1;
}

int main() {
   int a,b,c,d;
   scanf("%d %d %d %d", &a, &b, &c, &d);
   if(battle(a,b,c,d) == 1) {
      printf("Yes\n");
   }else {
      printf("No\n");
   }
   return 0;
}
