use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let mut a: Vec<u16> = s.split_whitespace().flat_map(str::parse).collect();
	a[0] = 0;
	a.sort();
	let s: u16 = a
		.windows(2)
		.map(|x| if x[1] - x[0] == 1 { 0 } else { x[1] })
		.sum();
	println!("{}", s)
}