#include<iostream>
#include<math.h>
#include<algorithm>
#include<stdint.h>
#include<vector>
#include<deque>
#include<stack>
#include<string>
#include<cstring>
#include<time.h>
#include<iomanip>
#include<list>
#include<set>
#include<unordered_map>
#include<unordered_set>
#include<random>
#include<bitset>
#include <queue>
#include <map>


using namespace std;
using ll = long long;
using ull = unsigned long long;
using uint = unsigned int;
using ldouble = long double;

#define repi(i,a,b) for(ll i = (a); i < (b); i++)
#define rep(i, n) for(ll i = 0; i < (n); ++i)
ll MOD = 1000000007;
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;
        }
    }
    return 0;
}

