#include <iostream>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>

static const int MOD = 1000000007;
using ll = int64_t;
using u32 = uint32_t;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max()/32*15+208;

int main() {
    int n, m, x, y;
    cin >> n >> m >> x >> y;
    x = (x-1)%(2*m), y = (y-1)%(2*m);
    puts((x == y || x+y+1 == 2*m) ? "YES" : "NO");
    return 0;
}