#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ul = unsigned long;
using ull = unsigned long long;

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int n;
	cin >> n;

	stack<ll> st;
	for (int i = 0; i < n; ++i)
	{
		string s;
		cin >> s;

		if (s == "+" || s == "-")
		{
			ll b = st.top();
			st.pop();
			ll a = st.top();
			st.pop();
			if (s == "-")
				b *= -1;
			st.push(a + b);
		}
		else
			st.push(stoll(s));
	}

	cout << st.top() << "\n";

	return 0;
}