#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
typedef int64_t Int;

int main(){
    int A, B, C, D;
    cin >> A >> B >> C >> D;

    while(true){
        C -= B;
        if(C <= 0) {cout << "Yes" << endl; return 0;}
        A -= D;
        if(A <= 0) {cout << "No" << endl; return 0;}
    }
}