#include <iostream>
#include <vector>
#include <fstream>

class StackMaxEffective {

public:

    void push(const int element) {
        elements_.push_back(element);

        max_elements_.empty() ? max_elements_.push_back(element) : max_elements_.push_back(std::max(element, max_elements_.back()));
    }

    void pop() {
        if (elements_.empty()) {
            std::cout << "error" << std::endl;
        }
        else {
            elements_.pop_back();
            max_elements_.pop_back();
        }
    }

    void get_max() {
        if (elements_.empty()) {
            std::cout << "None" << std::endl;
        }
        else {
            std::cout << max_elements_.back() << std::endl;
        }
    }

    void top() {
        if (elements_.empty()) {
            std::cout << "error" << std::endl;
        }
        else {
            std::cout << elements_.back() << std::endl;
        }
    }

private:

    std::vector<int> elements_;
    std::vector<int> max_elements_;
};

int main() {

    std::ifstream fin("input.txt");

    std::string command;
    int count, num;

    fin >> count;

    StackMaxEffective stack;

    for (int i = 0; i < count; i++) {
        fin >> command;
        if (command == "pop") {
            stack.pop();
        }
        if (command == "push") {
            fin >> num;
            stack.push(num);
        }
        if (command == "get_max") {
            stack.get_max();
        }
        if (command == "top") {
            stack.top();
        }
    }
}