#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>
#include <algorithm>
#include <math.h>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <bitset>

#define _GLIBCXX_DEBUG
#define rep(i, n) for (int64_t i = 0; i < (int64_t)(n); i++)
using namespace std;
using vi = vector<int64_t>;
using vvi = vector<vi>;

int main(int argc, const char * argv[]) {
    // fasten cin
    cin.tie(0);
    ios::sync_with_stdio(false);
    // implement
    int64_t a, b, c, d;
    cin >> a >> b >> c >> d;
    string res;
    for(int64_t i=0; i<107; i++){
        c -= b;
        if(c<=0){
            res = "Yes";
            break;
        }
        a -= d;
        if(a<=0){
            res = "No";
            break;
        }
    }
    cout << res << endl;
}
