using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (q, y) = (c[0], c[1]);
        var s = ReadLine().Split();
        var min = Calc(s, 0);
        var max = Calc(s, y);
        if (min > y || max < y)
        {
            WriteLine(-1);
            return;
        }
        var ng = -1L;
        var ok = y;
        while (ok - ng > 1)
        {
            var mid = (ok + ng) / 2;
            if (Calc(s, mid) >= y) ok = mid;
            else ng = mid;
        }
        if (Calc(s, ok) == y) WriteLine(ok);
        else WriteLine(-1);
    }
    static long Calc(string[] s, long x)
    {
        var stack = new Stack<long>();
        foreach (var si in s)
        {
            if (si == "+")
            {
                stack.Push(stack.Pop() + stack.Pop());
            }
            else if (si == "min")
            {
                stack.Push(Math.Min(stack.Pop(), stack.Pop()));
            }
            else if (si == "max")
            {
                stack.Push(Math.Max(stack.Pop(), stack.Pop()));
            }
            else if (si == "X")
            {
                stack.Push(x);
            }
            else
            {
                stack.Push(long.Parse(si));
            }
        }
        return stack.Pop();
    }
}