l1=[1,2,5,6]
l2=[7, 1, 3, 5, 6]
def find_missing_number(l1):
max_n=max(l1)+1
min_n=min(l1)
c=[a for a in range(min_n,max_n) ]
missing_n=[a for a in c if a not in l1]
return missing_n
print(find_missing_number(l1))
print(find_missing_number(l2))
[3, 4]
[2, 4]