#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

inline bool is_digit(string s) {
  return all_of(s.begin(), s.end(), ::isdigit);
}

int main() {
  int n;
  cin >> n;
  vector<string> s(n);
  rep(i, n) cin >> s[i];
  vector<int> q;
  rep(i, n) {
    if (is_digit(s[i])) q.push_back(stoi(s[i]));
    else {
      if (s[i] == "+") {
        int a = q.back();
        q.pop_back();
        int b = q.back();
        q.pop_back();
        q.push_back(a + b);
      }
      else if (s[i] == "-") {
        int a = q.back();
        q.pop_back();
        int b = q.back();
        q.pop_back();
        q.push_back(b - a);
      }
      else {
        assert(false);
      }
    }
  }
  assert(q.size() == 1);
  cout << q[0] << endl;
  return 0;
}