#!/usr/bin/env python3
n, m = map(int,input().split())
x, y = map(int,input().split())
def f(i):
    i = (i-1) % (2*m)
    if i >= m:
        i = (2*m-i-1) % m
    return i
print(f(x) == f(y) and 'YES' or 'NO')