#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
using namespace std;

#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl

#define INF 1<<30

int n,m;

int cl(int i){
    i = (i-1)%(2*m)+1;
    if(i<=m) return i;
    else return 2*m-i+1;
}

int main(){
    int x,y;
    cin>>n>>m>>x>>y;

    if(cl(x) == cl(y)) cout<<"YES"<<endl;
    else cout<<"NO"<<endl;

    return 0;
}