fn main() {
    let mut buf = String::new();
    let mut input = {
        use std::io::Read;
        std::io::stdin().read_to_string(&mut buf).unwrap();
        buf.split_whitespace()
    };

    let n: usize = input.next().unwrap().parse().unwrap();
    let a: Vec<u64> = (0..n)
        .map(|_| input.next().unwrap().parse().unwrap())
        .collect();

    let a_max = a.iter().fold(0, |acc, &x| acc.max(x));

    let a_2_max_len = format!("{:#b}", a_max).chars().skip(2).count();

    let a_2 = a
        .iter()
        .map(|x| {
            format!("{:#0width$b}", x, width = a_2_max_len + 1 + 2)
                .chars()
                .skip(2)
                .collect::<String>()
        })
        .collect::<Vec<_>>();

    let mut count = vec![0; a_2_max_len + 1];
    for i in 0..n {
        for (j, c) in a_2[i].chars().rev().enumerate() {
            if c == '1' {
                count[j] += 1;
            }
        }
    }

    let mut ans_2 = String::new();
    for j in 0..count.len() {
        if count[j] == 0 {
            ans_2.push('1');
            break;
        } else {
            ans_2.push('0');
        }
    }
    ans_2 = ans_2.chars().rev().collect();

    let ans = u64::from_str_radix(&ans_2, 2).unwrap();

    println!("{}", ans);
}