#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
    
    int n,m,x,y;scanf("%d%d%d%d",&n,&m,&x,&y);
    int numx=x/m,numy=y/m,rnkx=x%m,rnky=y%m;
    int ansx=0,ansy=0;
    if(numx%2==1)
    {
        if(rnkx==0)ansx=m;
        else ansx=m-rnkx+1;
    }
    else
    {
        if(rnkx==0)ansx=1;
        else ansx=rnkx;
    }
    if(numy%2==1)
    {
        if(rnky==0)ansy=m;
        else ansy=m-rnky+1;
    }
    else
    {
        if(rnky==0)ansy=1;
        else ansy=rnky;
    }
    if(ansx%m==ansy%m)printf("YES");
    else printf("NO");
    return 0;
}