#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
#define debug(x) std::cout << #x << ": " << x << '\n';
signed main() {
    #ifdef HOME
    freopen("input.txt", "r", stdin);
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif

    int n;
    cin >> n;

    vector <int> a;
    while (n--) {
        string s;
        cin >> s;

        if (s == "+") {
            int x = a.back();
            a.pop_back();
            int y = a.back();
            a.pop_back();
            a.app(x+y);
        }
        else if (s == "-") {
            int x = a.back();
            a.pop_back();
            int y = a.back();
            a.pop_back();
            a.app(y-x);
        }
        else {
            int x = stoi(s);
            a.app(x);
        }   
    }

    #ifdef HOME
    debug(a.size());
    #endif

    cout << a.back() << endl;
}