#include "bits/stdc++.h"
using namespace std;
#define int long long
#define REP(i, n) for (int i = 0; i < (int)n; ++i)
#define RREP(i, n) for (int i = (int)n - 1; i >= 0; --i)
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; --i)
#define ALL(a) a.begin(), a.end()
#define IN(a, x, b) (a <= x && x < b)
template<class T>inline void out(T t){cout << t << "\n";}
template<class T,class... Ts>inline void out(T t,Ts... ts){cout << t << " ";out(ts...);}
template<class T>inline bool CHMIN(T&a,T b){if(a > b){a = b;return true;}return false;}
template<class T>inline bool CHMAX(T&a,T b){if(a < b){a = b;return true;}return false;}
constexpr int INF = 1e18;

using T = tuple<int, int, int>;

signed main(){
	int N;
	cin >> N;
	vector<int>v;
	REP(i, N) {
		string s;
		cin >> s;
		if(s == "+") {
			int a = v.back();
			v.pop_back();
			v.back() += a;
		} else if(s == "-") {
			int a = v.back();
			v.pop_back();
			v.back() -= a;
		} else {
			v.emplace_back(stoll(s));
		}
	}
	out(v.back());
}