use std::collections::HashSet;

fn missing_integer(a: &[i64]) -> i64 {
    let mut vals: Vec<i64> = a.iter().copied().collect::<HashSet<_>>().into_iter().collect();
    vals.sort();

    let mut min = 1i64;
    for v in vals {
        if v > 0 {
            if min != v {
                break;
            }
            min += 1;
        }
    }

    min
}