#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max()/32*15+208;

int main() {
    int n;
    cin >> n;
    stack<int> A;
    for (int i = 0; i < n; ++i) {
        string s;
        cin >> s;
        if(isdigit(s[0])) A.emplace(stoi(s));
        else {
            int b = A.top(); A.pop();
            int a = A.top(); A.pop();
            A.emplace(s[0] == '+' ? a+b : a-b);
        }
    }
    cout << A.top() << "\n";
    return 0;
}