/* http://www.cs.nyu.edu/courses/summer07/G22.2110-001/hw07-java-driver.txt
 * Rename this file into Driver.java, and the other files for this example
 * into IntVector.java and IntStack.java. Compile with
 *     javac Driver.java
 * then run with
 *     java Driver
 * Enter commands like "push 3", "pop", or "quit".
 */
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Driver {
  public static void main(String[] args) throws IOException {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    IntStack b = new IntStack();
    while (true) {
      String line = in.readLine();
      if (null == line)
        break;
      StringTokenizer tokens = new StringTokenizer(line);
      String command = tokens.nextToken();
      if ("push".equals(command)) {
        int value = Integer.parseInt(tokens.nextToken());
        b.push(value);
        System.out.println("--> void");
      } else if ("pop".equals(command)) {
        int value = b.pop();
        System.out.println("--> " + value);
      } else if ("size".equals(command)) {
        System.out.println("--> " + b.size());
      } else if ("quit".equals(command)) {
        break;
      }
    }
  }
}