class Calc
    def initialize
	@stack = []
    end

    def push (n)
	@stack.push(n)
    end

    def add
	x = @stack.pop
	y = @stack.pop
	z = x + y
	@stack.push(z)
    end

    def mul
	x = @stack.pop
	y = @stack.pop
	z = x * y
	@stack.push(z)
    end

    def sub
	x = @stack.pop
	y = @stack.pop
	z = y - x
	@stack.push(z)
    end

    def div
	x = @stack.pop
	y = @stack.pop
	z = y / x
	@stack.push(z)
    end

    def top
	return @stack.last
    end
end