N,M = map(int, input().split())
x,y = map(int, input().split())
if x>y:
    x,y = y,x
if (y-x)%(2*M)==0:
    print("YES")
else:
    y1 = y%M
    x1 = x%M
    if y-x>=M and(y1+x1)%M==1:
        print("YES")
    else:
        print("NO")