#include <iostream>
#include <stack>
using namespace std;
int main(){
    int n;cin>>n;
    stack<int> A;
    for(int i = 0; n > i; i++){
        string s;cin>>s;
        if(s == "+"){
            int a = A.top();A.pop();
            int b = A.top();A.pop();
            A.push(a+b);
        }else if(s == "-"){
            int a = A.top();A.pop();
            int b = A.top();A.pop();
            A.push(a-b);
        }else{
            A.push(stoi(s));
        }
    }
    cout << A.top() << endl;
}