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

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var s = ReadLine();
        var c = NList;
        if (n % 2 == 1)
        {
            WriteLine(-1);
        }
        else
        {
            WriteLine(Math.Abs(n / 2 - s.Count(si => si == '(')));
        }
    }
}