use std::io::Read;

fn r(p: &mut Vec<&str>) -> i64 {
	let s = p.pop().unwrap();
	match s {
		"+" => r(p) + r(p),
		"-" => -r(p) + r(p),
		_ => s.parse().unwrap(),
	}
}

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let mut s: Vec<_> = s.split_whitespace().skip(1).collect();
	println!("{}", r(&mut s));
}