#include <iostream>
#include <string>
#include <sstream>
using namespace std;

template <class T>
struct Node {
    T data;
    Node<T> *next = NULL;
};

template <class T>
struct Queue {
    Node<T> *front = NULL;
    Node<T> *rear = NULL;
    int size = 0;
};

template <class T>
bool isEmpty(Queue<T> *q) {
    return (q->size == 0);
}

template <class T>
void enqueue(Queue<T> *q, T newData) {
    Node<T> *newNode = new Node<T>;
    newNode->data = newData;
    if (isEmpty(q)) {
        q->front = newNode;
    }
    else q->rear->next = newNode;
    q->rear = newNode;
    q->size += 1;
    return;
}

template <class T>
bool dequeue(Queue<T> *q, T &dataOut) {
    if (isEmpty(q)) return false;
    dataOut = q->front->data;
    Node<T> *temp = q->front;
    if (q->size == 1) q->rear = NULL;
    q->front = temp->next;
    q->size -= 1;
    delete temp; temp = NULL;
    return true;
}

template <class T>
void print(Queue<T> *q) {
    if (isEmpty(q)) return;
    Node<T> *temp = q->front;
    while (temp != NULL) {
        cout << temp->data << endl;
        temp = temp->next;
    }
    cout << endl;
}

template <class T>
void freeMemory(Queue<T> *&q) {
    Node<T> *temp = q->front;
    while (temp != NULL) {
        Node<T> *next = temp->next;
        delete temp;
        temp = next;
    }
    q->front = NULL;
    q->rear = NULL;
    q->size = 0;
}

void expressionCalculate(string expression) {
    reverse(expression.begin(), expression.end());
    stringstream ss;
    ss << expression;
    Queue<string> *queue = new Queue<string>;
    string str;
    while (!ss.eof()) {
        ss >> str;
        if (str != "") enqueue(queue, str);
        str.clear();
    }
    while (queue->size > 1) {
        dequeue(queue, str);
        if (str != "+" && str != "-" && str != "*" && str != "/") enqueue(queue, str);
        else {
            if ((queue->front->data == "+" || queue->front->data == "-" || queue->front->data == "*" || queue->front->data == "/")
                || (queue->front->next->data == "+" || queue->front->next->data == "-" || queue->front->next->data == "*" || queue->front->next->data == "/")) {
                enqueue(queue, str);
            }
            else {
                string str1;
                dequeue(queue, str1);
                double x = stod(str1);
                dequeue(queue, str1);
                double y = stod(str1);
                double z;
                if (str == "+") {
                    z = x + y;
                }
                else if (str == "-") {
                    z = y - x;
                }
                else if (str == "*") {
                    z = x * y;
                }
                if (str == "/") {
                    z = y / x;
                }
                str1 = to_string(z);
                enqueue(queue, str1);
            }
        }
    }
    dequeue(queue, str);
    cout << str << endl;
    delete queue;
    queue = NULL;
}

int main() {
    expressionCalculate("6 3 / 1 -");
    system("pause");
    return 0;
}