fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();

    let mut result: Vec<isize> = vec![];
    a.trim().split_whitespace().for_each(|s| {
        if s.parse::<isize>().is_ok() {
            result.push(s.parse().unwrap());
        } else {
            let a = result.pop().unwrap();
            let b = result.pop().unwrap();
            if s == "+" {
                result.push(a + b);
            } else {
                result.push(b - a);
            }
        }
    });
    println!("{}", result.pop().unwrap());
}