#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b;
    cin>>a>>b;
    a*=b;
    
    int c;
    cin>>c;
    c=a%c;
    
    int d;
    cin>>d;
    if(c+d==d)
    cout<<"YES"<<endl;
    else
    cout<<"NO"<<endl;
    
}