a,b=map(int,input().split())
c = []
n = []
n1= []
for i in range(a):
    for i in range(b):
        n1.append(input().split())
    n.append(n1)    
    n.remove(max(n))
    n.remove(min(n))
    ans = 0
    for j in n:
        ans += int(j)
    avg = ans / (b-2)
    c.append(avg)
print('%.2f'% max(c))