using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

class Nice {

	static string[] lines;
	static int getMn(int ind)
    {
		int res = 0;
		//246
		//6
		//64
		//642 oh no... fixing..
		int mn = 1;
		for(int i = ind; i>=0; i--)
        {
			if (Char.IsDigit(lines[1][i]))
				res += (int)((int)lines[1][i] - (int)'0') * mn;
			else
				break;
			mn *= 10;
        }
		return res;
    }
	static void Main(string[] args) {
		lines = File.ReadAllLines("input.txt");
		StreamWriter sw = new StreamWriter("output.txt");

		List<int> plus = new List<int>();
		List<int> minus = new List<int>();


		List<int> signs = new List<int>();
		int a = int.Parse(lines[0]);
		for (int i = 2; i < lines[1].Length; i++)
		{
			if(lines[1][i] == 'a' && lines[1][i-1] == '+' && lines[1][i-2] == '+' || lines[1][i] == '+' && lines[1][i - 1] == '+' && lines[1][i - 2] == 'a')
            {
				bool before = lines[1][i] == 'a';
				int slag = 1;
				if(i > 3)
					if(lines[1][i-3] == '*')
						slag = getMn(i - 4); //a++

				//sw.WriteLine(slag + " SLAG ");
				if (signs.Count > 0)
				{
					if (signs[signs.Count - 1] == 1)
						plus.Add(before ? slag : -slag);
					else
						minus.Add(before ? slag : -slag);
				} else
					plus.Add(before ? slag : -slag);
				if (i < lines[1].Length - 1)//сомнительное условие
					signs.Add(lines[1][i + 1] == '+' ? 1 : 0);
			}
		}
		int res = 0;

		//Todo correct sorting
		//Сначала все обычные единицы
		//потом минус единицы(где ++a)
		plus = plus.OrderBy(x => Math.Abs(x)).ToList();
		minus = minus.OrderBy(x => Math.Abs(x)).ToList();
		int ii = 0;
		int ij = plus.Count - 1;
		int ji = 0;
		int jj = minus.Count - 1;
		bool p = false;
		while (ii <= ij || ji <= jj)
        {
			if (a >= 0)
            {
				if(ji <= jj)
                {
					if (p) sw.Write(minus[jj] + " m ");
					if (minus[jj] > 0)
					{
						if (p) sw.Write((a + 1) + " AA ");
						res = res - (a + 1) * minus[jj];
						if (p) sw.WriteLine((a + 1) * minus[jj]);
					}
					else
					{
						if (p) sw.Write((a) + " AA ");
						res = res - (-a) * minus[jj];
						if(p) sw.WriteLine(-a * minus[jj]);
					}
					jj--;
				} else
                {
					if (p) sw.Write(plus[ii] + " p ");
					if (plus[ii] > 0)
					{

						if (p) sw.Write((a + 1) + " AA ");
						res = res + (a + 1) * plus[ii];
						if (p) sw.WriteLine((a + 1) * plus[ii]);
					}
					else
					{
						if (p) sw.Write((a) + " AA ");
						res = res + (-a) * plus[ii];
						if (p) sw.WriteLine(-a * plus[ii]);
					}
					ii++;
				}
            } else
            {
				if (ji <= jj)
				{
					if (p) sw.Write(minus[jj] + " m ");
					if (minus[jj] > 0)
					{
						if (p) sw.Write((a + 1) + " AA ");
						res = res - (a + 1) * minus[jj];
						if (p) sw.WriteLine((a + 1) * minus[jj]);
					}
					else
					{
						if (p) sw.Write((a) + " AA ");
						res = res - (-a) * minus[jj];
						if (p) sw.WriteLine(-a * minus[jj]);
					}
					jj--;
				}
				else
				{

					if (p) sw.Write(plus[ii] + " p ");
					if (plus[ii] > 0)
					{
						if (p) sw.Write((a + 1) + " AA ");
						res = res + (a + 1) * plus[ii];
						if (p) sw.WriteLine((a + 1) * plus[ii]);
					}
					else
					{
						if (p) sw.Write((a) + " AA ");
						res = res + (-a) * plus[ii];
						if (p) sw.WriteLine(-a * plus[ii]);
					}
					ii++;
				}
			}

			a++;
        }
		/*for (int i = minus.Count - 1; i >= 0; i--)
		{
			//sw.Write(minus[i] + "  ");
			if (minus[i] > 0)
			{
				res -= (a + 1) * minus[i];
				//sw.WriteLine((a + 1) * minus[i]);
			}
			else
			{
				res -= -a * minus[i];
				//sw.WriteLine(-a * minus[i]);
			}
			a++;
		}
		//sw.WriteLine("now +:");
		for (int i = 0; i < plus.Count; i++)
		{
			//sw.Write(plus[i] + "  ");
			if (plus[i] > 0)
			{
				res += (a + 1) * plus[i];
				//sw.WriteLine((a + 1) * plus[i]);
			}
			else
			{
				res += -a * plus[i];
				//sw.WriteLine(-a * plus[i]);
			}
			a++;
		}*/

		sw.Write(res);
		sw.Close();
	}
}