#include<bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("YES")
#define p_no() p("NO")

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N, M, X, Y;
    cin >> N >> M >> X >> Y;

    X--;
    Y--;

    X = X % (2*M);
    Y = Y % (2*M);

    // 2列違い
    if(X==Y){
        p_yes();
    }
    // 1列違い
    else if(X+Y==2*M-1){
        p_yes();
    }else{
        p_no();
    }
    
    return 0;
}