#include <iostream>

int main() {
    int n,m,x,y;
    std::cin >> n >> m >> x >> y;

    int a=(((x-1)/m)%2==0)?((x-1)%m+1):(m-(x-1)%m);
    int b=(((y-1)/m)%2==0)?((y-1)%m+1):(m-(y-1)%m);
    std::cout << (a==b?"YES":"NO") << std::endl;
}