// Finds the minimum, extracts it from the stack and returns it.
        public static int ExtractMin(Stack<int> s)
        {
            int min = FindMin(s);
            Extract<int>(s, min);
            return min;
        }
        // Extracts the first appearance of a value from a stack.
        public static void Extract<T>(Stack<T> s, T toExtract)
        {
            if(!s.IsEmpty())    // if empty nothing to extract
            {
                T val = s.Pop();
                if (val.Equals(toExtract))
                    return;     // dont re-insert if this is the wanted value
                Extract<T>(s, toExtract);   // check in rest of the stack
                s.Push(val);    // re-insert to keep stack
            }
        }
        // Finds and returns the minimum value in stack, without changing the stack.
        public static int FindMin(Stack<int> s)
        {
            int value = s.Pop();
            if (s.IsEmpty())    // if only value in stack
            {
                s.Push(value);
                return value;   // return it
            }
            int min = FindMin(s);   // find the minimum in rest of stack
            if (min > value)
                min = value;
            s.Push(value);  // re-insert to keep the stack
            return min;
        }