use std::cmp::min;

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 mut a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let asum: usize = a.iter().map(|i| *i).sum();

    let mut base: usize = 1;
    for i in 0..asum {
        if asum < i*(i+1)+i+1 {
            base = 2*(i-1) + 1;
            break;
        }
    }
    let mut pyramid: Vec<usize> = (0..base).map(|i| min(base/2+1, i+1) - if i > base/2 { i-base/2 } else { 0 }).collect();
    if base > n {
        (0..base-n).for_each(|_| a.push(0));
    } else if n > base {
        (0..n-base).for_each(|_| pyramid.push(0));
    }
    let result: usize = a.iter().zip(pyramid.iter())
        .map(|pair| if pair.0 > pair.1 { pair.0 - pair.1 } else { 0 })
        .sum()
    ;
    println!("{}", result);
}