#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  cin >> n;
  vector<int> stk;

  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;

    if (s == "+") {
      int x = stk.back(); stk.pop_back();
      int y = stk.back(); stk.pop_back();
      int z = x + y;
      stk.push_back(z);
    } else if (s == "-") {
      int x = stk.back(); stk.pop_back();
      int y = stk.back(); stk.pop_back();
      int z = y - x;
      stk.push_back(z);
    } else {
      stk.push_back(stoi(s));
    }
  }

  cout << stk.back() << endl;
  
  return 0;
}