#include <bits/stdc++.h>
using namespace std;

int main()
{
	int n;
	cin >> n;
	vector<string> a(n);
	for(int i = 0; i < n; i++) cin >> a[i];
	
	stack<int> stk;
	int v, v1, v2;
	for(int i = 0; i < n; i++)
	{
		if(a[i] != "+" && a[i] != "-")
		{
			v = stoi(a[i]);
			stk.push(v);
		}
		else
		{
			v1 = stk.top();
			stk.pop();
			v2 = stk.top();
			stk.pop();
			if(a[i] == "+") stk.push(v2 + v1);
			else stk.push(v2 - v1);
		}
	}
	cout << stk.top() << endl;
	return 0;
}