N,M = map(int, input().split())
x,y = map(int, input().split())
if x>y:
    x,y = y,x
if M==1 or (y-x)%(2*M)==0:
    print("YES")
else:
    q1 = y//M
    r1 = y%M
    if r1==0:
        q1 -= 1
    q2 = x//M
    r2 = x%M
    if r2==0:
        q2 -= 1
    if q1!=q2 and (r1+r2)%M==1:
        print("YES")
    else:
        print("NO")