n, m = [ int(v) for v in input().split() ]
a, b = [ int(v) for v in input().split() ]

a, b = a % (2*m), b % (2*m)
if a == 0:
    a = 2*m
if b == 0:
    b = 2*m


if a > m:
    a = 2*m + 1 - a
if b > m:
    b = 2*m + 1 - b

if a == b:
    print("YES")
else:
    print("NO")