a=int(input())
b=int(input())
c=[]
for i in range(a):
    c.append(int(input()))
c.sort()
if a%2==0:
    d=c[len(c)-1]+c[len(c)-2]/2
    e=(c[0]+c[1])/2
    print(d-e)
else:
    d=c[len(c)-1]
    e=(c[0]+c[1])/2
    print(d-e)