class Array
    def sum
        ans = 0
        for i in self
            ans += i
        end
        ans
    end

    def square
        ans = []
        for i in self
            ans << i * i
        end
        ans
    end

    def square!
        ans = []
        for i in 1 .. length - 1
            self[i] = self[i] * self[i]
        end
    end
end