fn get_primes(n: usize) -> Vec<bool> {
    let mut flgs = vec![true; n+1];
    flgs[0] = false;
    flgs[1] = false;

    for i in 2..=(n as f64).sqrt().ceil() as usize {
        if !flgs[i] { continue; }
        for j in i..=n/i {
            flgs[i*j] = false;
        }
    }

    flgs
}

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

    let LIMIT = 5000000;
    let primes = get_primes(LIMIT);
    let mut result = 0usize;
    let mut target = vec![false; 10];
    for i in 0..n { target[a[i]] = true; }
    let mut checked = vec![false; 10];
    let mut cnt = 0usize;
    let mut prev = 0usize;
    for i in 1..=LIMIT {
        if !primes[i] { continue; }
        let val = i.to_string().chars().map(|c| c as usize - '0' as usize).collect::<Vec<usize>>();
        if val.iter().filter(|&&v| !target[v]).count() > 0 {
            if cnt == n {
                let cval = i - prev - 2;
                result = result.max(cval);
            }
            checked = vec![false; 10];
            cnt = 0usize;
            prev = i;
            continue;
        }
        for &v in val.iter() {
            if !checked[v] {
                cnt += 1;
                checked[v] = true;
            }
        }
    }
    if cnt == n {
        let cval = LIMIT - prev - 1;
        result =result.max(cval);
    }
    if result == 0 {
        println!("-1");
    } else {
        println!("{}", result);
    }
}