# import sys
# sys.setrecursionlimit(10000)
def factorial(n):
    assert n>=0 and int(n) == n, "The number must be a positive integer only!"
    if n in [0, 1]:
        return 1
    else:
        return n * factorial(n-1)

# print(factorial(1.6))
# print(factorial(-2))
print(factorial(7))
