#include<bits/stdc++.h>
#define int long long
using namespace std;
int n,m,x,y,a,b,c,d,cx,cy;
signed main(){
//	freopen("class.in","r",stdin);
//	freopen("class.out","w",stdout);
	cin>>n>>m>>x>>y;
	a=(x-1)%m+1,b=(x-1)/m,c=(y-1)%m+1,d=(y-1)/m;
	cx=(b&1)?(m-a+1):a,cy=(d&1)?(m-c+1):c;
	printf("%s\n",cx==cy?"YES":"NO");
	return 0;
}