n, m = map(int, input().split())
x, y = map(int, input().split())

mod = 2 * m

rx = x % mod
ry = y % mod

if rx > m:
    rx = 2 * m - rx + 1
elif rx == 0:
    rx = 1

if ry > m:
    ry = 2 * m - ry + 1
elif ry == 0:
    ry = 1

if rx % mod == ry % mod:
    print("YES")
else:
    print("NO")