#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<queue>
#include<map>
#include<deque>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
typedef long long ll;
typedef pair<int,int> P;
template<class T> inline bool chmax(T&a , T b){ if(a<b){ a=b; return true; } else{ return false; } }
template<class T> inline bool chmin(T&a , T b){ if(a>b){ a=b; return true; } else{ return false; } } 

const int INF = 1e9;
const int MOD = 1e9+7;
const ll LINF = 1e18;

int main(){
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    while(1){
        c = c-b;
        if(c<=0){
            cout << "Yes" << endl;
            break;
        }
        a = a-d;
        if(a<=0){
            cout << "No" << endl;
            break;
        }
    }
    return 0;
}