using System;

public class Program

{

    public class Stack<T>

    {

        private class StackItem<TItem>

        {

            public TItem data;

            public StackItem<TItem> next;

            public StackItem(TItem data){

                this.data = data;

            }

        }

        private StackItem<T> top;

        public virtual void Push(T data)

        {

            var newItem = new StackItem<T>(data);

            newItem.next = top;

            top = newItem;

        }

        public virtual T Pop()

        {

            if (top == null) throw new Exception();

            var item = top;

            top = top.next;

            return item.data;

        }

        public T Peek()

        {

            if (top == null) throw new Exception();

            return top.data;

        }

        public bool IsEmpty(){

            return top == null;

        }

    }

    public class StackExtended : Stack<int>

    {

        private Stack<int> minStack = new Stack<int>();

        public override void Push(int data)

        {

            base.Push(data);

            if (minStack.IsEmpty() || minStack.Peek() >= data)

            {

                minStack.Push(data);

            }

        }

        public override int Pop()

        {

            var popped = base.Pop();

            if (!minStack.IsEmpty() && popped == minStack.Peek())

            {

                minStack.Pop();

            }

            return popped;

        }

        public int Min()

        {

            if (minStack.IsEmpty()) return -1;

            return minStack.Peek();

        }

    }

    public static void Main()

    {

        var stack = new StackExtended();

        stack.Push(1);

        stack.Push(2);

        stack.Push(3);

        stack.Push(-90);

        Console.WriteLine("MIN: " + stack.Min());

        while(!stack.IsEmpty())

        {

            Console.WriteLine(stack.Pop());

        }

    }

}