#include<stdio.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main(){
 int A,B, C, D;
 scanf("%d %d %d %d", &A, &B, &C, &D);
 int TAKAHASI = C/B;
 int AOKI = A/D;
 if( AOKI > TAKAHASI){
  printf("Yes\n");
 }else{
  printf("No\n");
 }
  return 0;
}