from sys import stdin

def solve():
    n, m = map(int, input().split())
    x, y = map(int, input().split())
    x, y = x - 1, y - 1

    ans = 'YES' if furiwake(m, x) == furiwake(m, y) else 'NO'

    print(ans)

def furiwake(m, x):
    if (x // m) & 1:
        return m - 1 - (x % m)
    else:
        return x % m

def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

if __name__ == '__main__':
    solve()