#include <iostream>
#include <vector>
#include <string>
#include <stack>
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> st;
	for (int i = 0; i < N; i++){
		if (A[i] == "+" || A[i] == "-"){
			int b = st.top();
			st.pop();
			int a = st.top();
			st.pop();
			if (A[i] == "+"){
				st.push(a + b);
			}
			if (A[i] == "-"){
				st.push(a - b);
			}
		} else {
			st.push(stoi(A[i]));
		}
	}
	cout << st.top() << endl;
}