using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var opCodes = new int[] { 1, 5, 1, 7, 3, 2, 0 };

        var instructionPointer = 0;

        var stack = new Stack<int>();

        while(true) {

            var instruction = opCodes[instructionPointer++];

            switch(instruction) {

                case 1: {

                    //pushint

                    var value = opCodes[instructionPointer++];

                    stack.Push(value);

                }

                break;

                case 2: {

                    var value = stack.Pop();

                    Console.WriteLine(value);

                }

                break;

                case 3: {

                    var value1 = stack.Pop();

                    var value2 = stack.Pop();

                    var result = value1 + value2;

                    stack.Push(result);

                }

                break;

                case 0:

                    return;

            }

        }

    }

}