use std::cmp::Reverse;


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

    let mut result = 0usize;
    let mut exp = p.iter().sum::<usize>();
    let mut p = (0..n).map(|i| (i+1, p[i])).collect::<Vec<_>>();
    p.sort_by_key(|&(_, v)| Reverse(v));
    for &(i, _) in p.iter() {
        if exp > 2*i {
            result = result.max(exp - 2*i);
        }
        exp -= i;
    }
    println!("{}", result);
}