#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define p(s) cout<<(s)<<endl
#define REP(i,n,N) for(int i=n;i<N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=n;i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define F first
#define S second
typedef long long ll;
using namespace std;
const int inf=1e9+7;

int N, M;
int X, Y;
int main(){
    cin>>N>>M>>X>>Y;
    if(X%(2*M)==Y%(2*M)||(2*M-X+1)%(2*M) == Y%(2*M)){
        p("YES");
    }else{
        p("NO");
    }
    return 0;
}