// 1 zadacha

#include <iostream>
#include <cstring>
using namespace std;

//const int MAX = 100;

class Stack
{
    int current; //индекс на върха на стека
    int capacity; //колко елемента има в стека
    int * elements; //елементите на стека

    void copyStack(const Stack& other)
    {
        current = other.current;
        capacity = other.capacity;
        elements = new int[capacity];
        for(int i = 0; i < capacity; i++)
            elements[i] = other.elements[i];
    }
    void deleteStack()
    {
        delete [] elements;
    }
    void resize()
    {
        int newSize = capacity*2;
        int* helper = new int [capacity];
        for (int i = 0; i < capacity; i++)
        {
            helper[i] = elements[i];
        }
        delete[] elements;
        elements = new int[newSize];
        for (int i = 0; i < capacity; i++)
        {
            elements[i] = helper[i];
        }
        capacity = newSize;
        delete[] helper;
    }
public:
    Stack()
    {
        current = -1;
        capacity = 10;
        elements = new int[capacity];
    }
    Stack(const Stack& other)
    {
        copyStack(other);
    }
    Stack& operator=(const Stack& other)
    {
        if(this != &other)
        {
            deleteStack();
            copyStack(other);
        }
        return *this;
    }
    bool isEmpty()
    {
        return current < 0;
    }
    bool isFull()
    {
        return current == capacity - 1;
    }
    int numOfElements()
    {
        return current+1;
    }
    void push(int element)
    {
        if(isFull())
            resize();

        elements[++current] = element;
    }
    void pop()
    {
        if(!isEmpty())
        {
            current--;
            capacity--;
        }
        else
            cout << "The stack is empty!";
    }
    int peek() //top()
    {
        if(!isEmpty())
            return elements[current];
        else
            cout << "The stack is empty.";
    }
    friend ostream& operator<<(ostream& os, const Stack& s)
    {
        for (int i = 0; i < s.capacity; i++)
        {
            os << s.elements[i] << " ";
        }
        return os;
    }
};

int calculate(char str[])
{
    Stack st;
    int n = strlen(str);
    for(int i = 0; i < n; )
    {
        if(str[i] == ' ') i++;
        if(str[i] >= '0' && str[i] <= '9')
        {
            st.push(str[i] - 48);
            i++;
        }
        else if(str[i] == '+')
        {
            if(st.numOfElements() < 2) return -1;
            else
            {
                int x = st.peek();
                st.pop();
                int y = st.peek();
                st.pop();
                int z = x + y; //cout << z << endl;
                st.push(z);
                i++;
            }
        }
        else if(str[i] == '-')
        {
            if(st.numOfElements() < 2) return -1;
            else
            {
                int x = st.peek();
                st.pop();
                int y = st.peek();
                st.pop();
                int z = y - x; //cout << z << endl;
                st.push(z);
                i++;
            }
        }
        else if(str[i] == '*')
        {
            if(st.numOfElements() < 2) return -1;
            else
            {
                int x = st.peek();
                st.pop();
                int y = st.peek();
                st.pop();
                int z = x * y; //cout << z << endl;
                st.push(z);
                i++;
            }
        }
        else if(str[i] == '/')
        {
            if(st.numOfElements() < 2) return -1;
            else
            {
                int x = st.peek();
                st.pop();
                int y = st.peek();
                st.pop();
                if(x == 0) return -1;
                else
                {
                    int z = y / x; //cout << z << endl;
                    st.push(z);
                    i++;
                }
            }
        }
        else if(str[i] == '%')
        {
            if(st.numOfElements() < 2) return -1;
            else
            {
                int x = st.peek();
                st.pop();
                int y = st.peek();
                st.pop();
                if(x == 0) return -1;
                else
                {
                    int z = y % x; //cout << z << endl;
                    st.push(z);
                    i++;
                }
            }
        }
    }
    if(st.numOfElements() == 1)
        return st.peek();
    else return -1; // wrong input
}

int main()
{
    char expr[101];
    cin.getline(expr,101);
    cout << calculate(expr);
    return 0;
}