#include<bits/stdc++.h>
//if atcoder
//#pragma GCC optimize(3)
#define FastIO ios::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define int long long
#define I using
#define AK namespace
#define CSPS2025 std
I AK CSPS2025;
const int maxn=1e6+10,maxm=1e3+10,mod=998244353;
int t,n,m,x,y,u,v,w,arr[maxn];
signed main()
{
    
        cin>>n>>m>>x>>y;
        if((n+m-2)%(x+1)==y)
        {
            cout<<"NO\n";
        }
        else
        {
            cout<<"YES\n";
        }
    
    return 0;
}