#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef long double ld;

#define rep(i,s,n) for(ll (i)=(s);(i)<(n);(i)++)
#define repd(i,s,n) for(ll (i)=(n-1);(i)>=(s);(i)--)
#define FOR(i,s,n) for(ll (i)=(s);(i)<=(n);(i)++)
#define all(x) x.begin(),x.end()
#define size(x) ((ll)(x).size()
#define PB push_back

int main(){
   int a,b,c,d;
   cin >> a >> b >> c >>d;
   while(a>0 && c>0){
     a=a-d;
     c=c-d;
   }
   if(a>b){
       cout << "Yes" << endl;
   }else{
       cout << "No" << endl;
   }
   return 0;
}
