use std::io::Read;

fn main() {
	let mut s = String::new();
	std::io::stdin().read_to_string(&mut s).ok();
	let mut n: Vec<u64> =
		s.split_whitespace().skip(1).flat_map(str::parse).collect();
	n.sort();
	let mut a = 0;
	for b in n.chunks(2) {
		a += b[1] * b[0];
	}
	println!("{a}")
}