#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int N;
string A[1010];
int a1, a2, ans;
stack<int> st;

int main() {
  cin >> N;
  for (int i = 0; i < N; i++) cin >> A[i];
  for (int i = 0; i < N; i++) {
    if (A[i] == "+" || A[i] == "-") {
      a2 = st.top(); st.pop();
      a1 = st.top(); st.pop();
      if (A[i] == "+") ans = a1 + a2;
      if (A[i] == "-") ans = a1 - a2;
      st.push(ans);
    } else {
      ans = stoi(A[i]);
      st.push(ans);
    }
  }
  cout << st.top() << endl;
}