import sys
from typing import List, Tuple


def int1(x: str, /): return int(x) - 1


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    n, m = map(int, input().split())
    x, y = map(int1, input().split())
    x, y = x % (2 * m), y % (2 * m)
    return 'YES' if x + y == 2 * m - 1 or x == y else 'NO'


def _start():
    ret = main()

    if ret is not None:
        if isinstance(ret, List) or isinstance(ret, Tuple):
            print(*ret)
        else:
            print(ret)


if __name__ == '__main__':
    _start()