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

int main(){
    int n;
    cin >> n;
    vector<ll> ans;
    for(int i = 0; i < n; i++){
        string s;
        cin >> s;
        if(s == "+"){
            ans.rbegin()[1] += ans.back();
            ans.pop_back();
        }else if(s == "-"){
            ans.rbegin()[1] -= ans.back();
            ans.pop_back();
        }else{
            ans.push_back(stoi(s));
        }
    }
    cout << ans[0] << '\n';
}