#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
#define ITR(i,c) for(auto i=begin(c);i!=end(c);i++)
#define FORE(x,arr) for(auto &x:arr)
#define FOR(i,a,n) for(int i=a;i<(int)(n);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(c) begin(c),end(c)
const int DX[4]={0,1,0,-1}, DY[4]={-1,0,1,0};
const int INF = 1e9;

int main(int argc, char const *argv[]) {
    int N,M,X,Y;
    cin >> N >> M >> X >> Y;
    X--; Y--;
    int a,b;
    if((X/M)%2==0) {
        a = 1+X%M;
    }
    else {
        a = M-X%M;
    }
    if((Y/M)%2==0) {
        b = 1+Y%M;
    }
    else {
        b = M-Y%M;
    }

    if(a==b) cout << "YES" << endl;
    else cout << "NO" << endl;
    return 0;
}