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

int main() {

    int n;
    cin >> n;

    stack<int> st;

    for(int i = 0; i < n; ++i) {
        string p;
        cin >> p;
        if(p == "+" || p == "-") {
            int b = st.top();
            st.pop();
            int a = st.top();
            st.pop();
            int c;
            if(p == "+")  c = a + b;
            else c = a - b;
            st.push(c);
        }
        else {
            int q = stoi(p);
            st.push(q);
        }
    }

    cout << st.top() << endl;
}