#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<(n);i++)


int main(void){
    ll n, m; cin >> n >> m;
    ll x, y; cin >> x >> y;
    ll mod = 2 * m;
    ll numx = x % mod;
    ll numy = y % mod;

    if(numx > m) numx = 2 * m - numx + 1;
    if(numx == 0) numx = 1;

    if(numy > m) numy = 2 * m - numy + 1;
    if(numy == 0) numy = 1;

    if(numx % mod == numy % mod) printf("YES\n");
    else printf("NO\n");
    return 0;
}