fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut t = String::new();
    std::io::stdin().read_line(&mut t).ok();
    let t: Vec<usize> = t.trim().split_whitespace().map(|s| s.parse::<usize>().unwrap() + 12usize).collect();

    let melody: Vec<usize> = vec![0,2,4,5,7,9,11];
    let result: Vec<usize> = (0..12)
        .filter(|i| n == t.iter().filter(|&v| melody.contains(&((v - i) % 12))).count())
        .collect();
    if result.len() == 1 {
        println!("{}", result[0]);
    } else {
        println!("{}", -1);
    }
}