#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using namespace std;


int main()
{
    int n;
    cin >> n;
    vector<long long> v;
    for (int i = 0; i < n; i++){
        string s;
        cin >> s;
        if (s[0] >= '0' && s[0] <= '9') v.push_back(stoll(s));
        else if (s == "-"){
            int t1, t2;
            t1 = v.back();
            v.pop_back();
            t2 = v.back();
            v.pop_back();
            v.push_back(t2 - t1);
        } else {
            int t1, t2;
            t1 = v.back();
            v.pop_back();
            t2 = v.back();
            v.pop_back();
            v.push_back(t2 + t1);
        }
    }
    cout << v[0] << endl;
}