N, M = map(int, input().split())
X, Y = map(int, input().split())

def cal(x):
    a = (x - 1) % (M * 2)
    if a >= M:
        a = 2 * M - a - 1
    return a

if cal(X) == cal(Y):
    print("YES")
else:
    print("NO")