use std::io::Read;

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