#include <iostream>
#include <algorithm>
#include <bitset>
#include <math.h>
#include <string>
#include <map>
#include <vector>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i, n) for (int i = 0; i < n; i++)
#define LargeNum 1000000007
typedef pair <double, double> P;

int main(){
    int A, B, C, D, t, a;
    bool flag;
    cin >> A >> B >> C >> D;
    while(true){
        C -= B;
        if(C<=0) {
            flag=true;
            break;
        }
        A -= D;
        if(A<=0){
            flag=false;
            break;
        }
    }
    if(flag) cout << "Yes" << endl;
    else cout << "No" << endl;
    return 0;
}
