print("hello world!")

function fact (n)
    if n < 0 then
        print("factorial for a negative number is not defined!")
        os.exit()m
    elseif n == 0 then
        return 1
    else 
        return n * fact(n - 1)
    end
end

print("enter a number")
a = io.read("*n")
print(fact(a))