fn main() {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).ok();
	let n: Vec<u8> = s.split_whitespace().flat_map(str::parse).collect();
	let d = n[1] - n[0] + 2;
	println!("{}", d / 3 + d % 3 - 1);
}