#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{ vector<double> stack;

  while (true)
  { cout << " ? ";
    string t;
    cin >> t;

    // is t a number?
    if (t[0] >= '0' && t[0] <= '9')
    { double v = atof(t.c_str());
      stack.push_back(v); }

    else if (t == "+")
    { double b = stack.back();  stack.pop_back();
      double a = stack.back();  stack.pop_back();
      stack.push_back(a+b); }

    else if (t == "-")
    { double b = stack.back();  stack.pop_back();
      double a = stack.back();  stack.pop_back();
      stack.push_back(a-b); }

    else if (t == "*")
    { double b = stack.back();  stack.pop_back();
      double a = stack.back();  stack.pop_back();
      stack.push_back(a*b); }

    else if (t == "/")
    { double b = stack.back();  stack.pop_back();
      double a = stack.back();  stack.pop_back();
      stack.push_back(a/b); }

    cout << "Stack is";
    for (int i = 0; i < stack.size(); i += 1)
      cout << " " << stack.at(i);
    cout << "\n"; } }