Problem:
Score : 700 points

Problem Statement

We have N gemstones labeled 1 through N.

You can perform the following operation any number of times (possibly zero).

Select a positive integer x, and smash all the gems labeled with multiples of x.

Then, for each i, if the gem labeled i remains without getting smashed, you will receive a_i yen (the currency of Japan).
However, a_i may be negative, in which case you will be charged money.

By optimally performing the operation, how much yen can you earn?

Constraints

All input values are integers.

1 \leq N \leq 100

|a_i| \leq 10^9

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the maximum amount of money that can be earned.

Sample Input 1

6
1 2 -6 4 5 3

Sample Output 1

12

It is optimal to smash Gem 3 and 6.

Sample Input 2

6
100 -100 -100 -100 100 -100

Sample Output 2

200

Sample Input 3

5
-1 -2 -3 -4 -5

Sample Output 3

0

It is optimal to smash all the gems.

Sample Input 4

2
-1000 100000

Sample Output 4

99000

Solution in Rust (1.15.1) (judge verdict: Accepted)

#[allow(unused_imports)]
use std::cmp::{max, min, Ordering};
#[allow(unused_imports)]
use std::collections::{HashMap, HashSet, BinaryHeap, VecDeque, BTreeSet};
#[allow(unused_imports)]
use std::iter::FromIterator;
#[allow(unused_imports)]
use std::io::stdin;

mod util {
    use std::io::stdin;
    use std::str::FromStr;
    use std::fmt::Debug;

    #[allow(dead_code)]
    pub fn line() -> String {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.trim().to_string()
    }

    #[allow(dead_code)]
    pub fn gets<T: FromStr>() -> Vec<T>
    where
        <T as FromStr>::Err: Debug,
    {
        let mut line: String = String::new();
        stdin().read_line(&mut line).unwrap();
        line.split_whitespace()
            .map(|t| t.parse().unwrap())
            .collect()
    }
}

#[allow(unused_macros)]
macro_rules! get {
    ($t:ty) => {
        {
            let mut line: String = String::new();
            stdin().read_line(&mut line).unwrap();
            line.trim().parse::<$t>().unwrap()
        }
    };
    ($($t:ty),*) => {
        {
            let mut line: String = String::new();
            stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            (
                $(iter.next().unwrap().parse::<$t>().unwrap(),)*
            )
        }
    };
    ($t:ty; $n:expr) => {
        (0..$n).map(|_|
                    get!($t)
                   ).collect::<Vec<_>>()
    };
    ($($t:ty),*; $n:expr) => {
        (0..$n).map(|_|
                    get!($($t),*)
                   ).collect::<Vec<_>>()
    };
    ($t:ty ;;) => {
        {
            let mut line: String = String::new();
            stdin().read_line(&mut line).unwrap();
            line.split_whitespace()
                .map(|t| t.parse::<$t>().unwrap())
                .collect::<Vec<_>>()
        }
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}

struct Flow {
    // to, capacity, rev
    edges: Vec<Vec<(usize, usize, usize)>>,
}

impl Flow {
    fn new(max_size: usize) -> Flow {
        Flow { edges: vec![Vec::new(); max_size + 1] }
    }

    fn add_edge(&mut self, from: usize, to: usize, cap: usize) {
        let from_rev = self.edges[to].len();
        let to_rev = self.edges[from].len();

        self.edges[from].push((to, cap, from_rev));
        self.edges[to].push((from, 0, to_rev));
    }

    fn max_flow_dinic(&mut self, s: usize, t: usize) -> usize {
        let mut flow = 0;
        loop {
            let level = self.bfs_dinic(s);
            let mut iter = vec![0; self.edges.len()];
            if level[t].is_none() {
                return flow;
            }

            loop {
                let f = self.dfs_dinic(s, t, usize::max_value(), &level, &mut iter);
                if f == 0 {
                    break;
                }
                flow += f;
            }
        }
    }

    fn bfs_dinic(&self, s: usize) -> Vec<Option<usize>> {
        let mut level = vec![None; self.edges.len()];
        let mut que = VecDeque::new();

        level[s] = Some(0);
        que.push_back(s);

        while !que.is_empty() {
            let v = que.pop_front().unwrap();
            let l = Some(level[v].unwrap() + 1);

            for &(to, cap, _) in &self.edges[v] {
                if cap > 0 && level[to].is_none() {
                    level[to] = l;
                    que.push_back(to);
                }
            }
        }
        level
    }

    fn dfs_dinic(
        &mut self,
        v: usize,
        t: usize,
        f: usize,
        level: &[Option<usize>],
        iter: &mut [usize],
    ) -> usize {
        if v == t {
            return f;
        }

        for i in iter[v]..self.edges[v].len() {
            iter[v] = i;

            let (to, cap, rev) = self.edges[v][i];
            if cap > 0 && level[v].unwrap() < level[to].unwrap_or(0) {
                let d = self.dfs_dinic(to, t, min(f, cap), level, iter);
                if d > 0 {
                    self.edges[v][i].1 -= d;
                    self.edges[to][rev].1 += d;
                    return d;
                }
            }
        }
        0
    }

    fn max_flow_ff(&mut self, s: usize, t: usize) -> usize {
        let mut flow = 0;
        let l = self.edges.len();
        loop {
            let f = self.dfs_ff(s, t, usize::max_value(), &mut vec![false; l]);
            if f == 0 {
                break;
            }
            flow += f;
        }
        flow
    }

    fn dfs_ff(&mut self, v: usize, t: usize, f: usize, used: &mut [bool]) -> usize {
        if v == t {
            return f;
        }
        used[v] = true;

        for i in 0..self.edges[v].len() {
            let (to, cap, rev) = self.edges[v][i];
            if !used[to] && cap > 0 {
                let d = self.dfs_ff(to, t, min(f, cap), used);
                if d > 0 {
                    self.edges[v][i].1 -= d;
                    self.edges[to][rev].1 += d;
                    return d;
                }
            }
        }
        0
    }

    fn cut(&self, s: usize) -> BTreeSet<usize> {
        let mut stack = Vec::new();
        let mut ss = BTreeSet::new();
        ss.insert(s);
        stack.push(s);

        while !stack.is_empty() {
            let v = stack.pop().unwrap();
            for &(to, cap, _) in &self.edges[v] {
                if cap > 0 && !ss.contains(&to) {
                    ss.insert(to);
                    stack.push(to);
                }
            }
        }

        ss
    }
}

fn main() {
    let n = get!(usize);
    let a = util::gets::<i64>();

    let s = n + 1;
    let t = n + 2;

    let mut flow = Flow::new(n + 2);

    for (&x, i) in a.iter().zip(1..) {
        if x <= 0 {
            // flow.add_edge(s, i, x.abs() as usize);
            flow.add_edge(i, t, x.abs() as usize);
        } else {
            // flow.add_edge(i, t, x.abs() as usize);
            flow.add_edge(s, i, x.abs() as usize);
        }

        for k in (2..).map(|m| i * m).take_while(|&k| k <= n) {
            // flow.add_edge(i, k, usize::max_value());
            flow.add_edge(k, i, usize::max_value());
        }
    }

    println!(
        "{}",
        a.iter().filter(|&&x| x > 0).sum::<i64>() as usize - flow.max_flow_dinic(s, t)
    );

    // debug!(flow.cut(s));
}