#include <iostream>

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

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