#include <bits/stdc++.h>
using namespace std;
struct node {
  long long v;
  bool c;
} arr[12000];
bool comparator(node a, node b) { return a.v < b.v; }
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long i, j, p, v, l, n = 0, a, ans = 0;
  cin >> a;
  string s;
  cin >> s;
  l = s.length();
  s = '+' + s;
  for (i = 0; i < l; i += 3) {
    v = 0;
    p = s[i++] == '+' ? 1 : -1;
    if (s[i] >= '0' and s[i] <= '9')
      for (; s[i] >= '0' and s[i] <= '9'; i++) v = v * 10 + s[i] - 48;
    else
      v = 1;
    if (s[i] == '*') i++;
    n++;
    arr[n].v = v * p;
    arr[n].c = s[i] == 'a';
  }
  sort(arr + 1, arr + 1 + n, comparator);
  for (i = 1; i <= n; i++) {
    if (arr[i].c)
      ans += arr[i].v * a++;
    else
      ans += arr[i].v * ++a;
  }
  cout << ans << endl;
  return 0;
}
