#include <stdio.h>

int main() {
  int A=0,B=0,C=0,D=0;
  scanf("%d %d %d %d",&A,&B,&C,&D );
  while(1){
    C -= B;
    if(C<=0) break;
    A -= D;
    if(A<=0) break;
  }
  if(A<=0) printf("No\n");
  if(C<=0) printf("Yes\n");
  return 0;
}