#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll zero = 0;
ll INF = 10000000000;

int main(){
    int A,B,C,D;
    cin >> A>>B>>C>>D;
    if((A-1)/D >= (C-1)/B){
        printf("Yes");
    }
    else{
        printf("No");
    }
    //printf("%d\n", );
    
}