fn find_break(arr: &Vec) -> Option {
    arr.windows(2).find(|arr| arr[1] != arr[0] + 1).map(|arr| arr[1])
}

fn main() {
    println!("{}", match find_break(&vec![2, 3, 4, 5, 6, 7, 8]) {
        Some(s) => s,
        None => -1
    });
}
// Rust Options Some None using closures