#include<iostream>
#include<string>
#include<vector>
#include<sstream>
using namespace std;
int main()
{
    string a;
    vector<int> numbers;
    cin>>a;
    while(a!="end")
    {
        istringstream aIn(a);
        int num, operation;
        bool isNumber = aIn >> num;
        if(isNumber)
            numbers.push_back(num);
        else
        {
            if(a=="sum")
            {
                operation = numbers[numbers.size()-1] + numbers[numbers.size()-2];
                numbers.erase(numbers.end()-2, numbers.end());
                numbers.push_back(operation);
            }
            if(a=="subtract")
            {
                operation = numbers[numbers.size()-1] - numbers[numbers.size()-2];
                numbers.erase(numbers.end()-2, numbers.end());
                numbers.push_back(operation);
            }
            if(a=="concat")
            {
                operation = numbers[numbers.size()-1] + numbers[numbers.size()-2]*10;
                numbers.erase(numbers.end()-2, numbers.end());
                numbers.push_back(operation);
            }
            if(a=="discard")
            {
                numbers.erase(numbers.end()-1, numbers.end());
            }
        }
        cin>>a;
    }
    for(int i:numbers)
    {
        cout<<i<<endl;
    }
    return 0;
}