#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1e9;
int MOD = 1e9+7;
main(){
    int N,M,X[2];
    cin >> N >> M >> X[0] >> X[1];
    X[0]--,X[1]--;
    int a[2];
    for(int i = 0;i < 2;i++){
        if((X[i]/M)%2) a[i] = M - X[i]%M - 1;
        else a[i] = X[i]%M;
    }
    if(a[0] == a[1])cout << "YES" << endl;
    else cout << "NO" << endl;
}