#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0; i<n; i++)
#define eb(t) emplace_back(t)
typedef long long ll;
typedef long long unsigned int llu;
ll INF = 1000000009;
ll MOD = 1000000007;


void solve(){

    ll a,b,c,d;
    cin >> a >> b >> c >> d;
    bool b_;
    while(a>0&&b>0){
        c -= b;
        if(c<=0) {
            b_=true;
            break;
        }
        a -= d;
        if(a<=0){
            b_=false;
            break;
        }
    }

    if(b_) cout << "Yes" << endl;
    else cout << "No" << endl;

}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  return 0;
}
