#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define pint pair<int, int>
#define pll pair<ll, ll>
#define vint vector<int >
#define vll vector<ll >
#define ALL(x) (x).begin(), (x).end()
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i,n) for (int i = 0; i < (n); ++i)
const int INF = 100100100;
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;
int main(){
    int a,b,c,d;
    cin >> a >> b >> c >>d;
    REP(i,100){
        c-=b;
        if(c<=0){
            cout << "Yes" << endl;
            return 0;
        }
        a-=d;
        if(a<=0){
            cout << "No" << endl;
            return 0;
        }
    }
    return 0;
}