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

int main() {
    int n;
    if (!(cin >> n) || n < 1 || n > 1000) {
        cout << "Invalid input";
        return 0;
    }
    cin.ignore(); // skip newline after n

    int stack[5];  // stack with max size 5
    int top = -1;  // empty stack

    for (int i = 0; i < n; i++) {
        string line;
        getline(cin, line);
        stringstream ss(line);
        string cmd;
        ss >> cmd;

        if (cmd == "push") {
            int x;
            if (!(ss >> x) || !(ss.eof())) { // invalid integer or extra tokens
                cout << "Invalid input\n";
                return 0;
            }
            if (top >= 4) {  // stack full
                cout << "Stack overflow\n";
            } else {
                stack[++top] = x;
            }
        } else if (cmd == "peek") {
            string extra;
            if (ss >> extra) { // extra tokens invalid
                cout << "Invalid input\n";
                return 0;
            }
            if (top == -1) {
                cout << "Stack is empty\n";
            } else {
                cout << stack[top] << "\n";
            }
        } else {
            cout << "Invalid input\n";
            return 0;
        }
    }

    return 0;
}