Problem:
Score: 200 points

Problem Statement

Takahashi, who works at DISCO, is standing before an iron bar.
The bar has N-1 notches, which divide the bar into N sections. The i-th section from the left has a length of A_i millimeters.

Takahashi wanted to choose a notch and cut the bar at that point into two parts with the same length.
However, this may not be possible as is, so he will do the following operations some number of times before he does the cut:

Choose one section and expand it, increasing its length by 1 millimeter. Doing this operation once costs 1 yen (the currency of Japan).

Choose one section of length at least 2 millimeters and shrink it, decreasing its length by 1 millimeter. Doing this operation once costs 1 yen.

Find the minimum amount of money needed before cutting the bar into two parts with the same length.

Constraints

2 \leq N \leq 200000

1 \leq A_i \leq 2020202020

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 A_3 ... A_N

Output

Print an integer representing the minimum amount of money needed before cutting the bar into two parts with the same length.

Sample Input 1

3
2 4 3

Sample Output 1

3

The initial lengths of the sections are [2, 4, 3] (in millimeters). Takahashi can cut the bar equally after doing the following operations for 3 yen:

Shrink the second section from the left. The lengths of the sections are now [2, 3, 3].

Shrink the first section from the left. The lengths of the sections are now [1, 3, 3].

Shrink the second section from the left. The lengths of the sections are now [1, 2, 3], and we can cut the bar at the second notch from the left into two parts of length 3 each.

Sample Input 2

12
100 104 102 105 103 103 101 105 104 102 104 101

Sample Output 2

0

Solution in Rust (1.42.0) (judge verdict: Accepted)

#[allow(unused_macros, dead_code)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

#[allow(unused_macros, dead_code)]
macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };

    ($next:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

#[allow(unused_macros, dead_code)]
macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, bytes) => {
        read_value!($next, String).into_bytes()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

#[allow(dead_code)]
struct UnionFind {
    parent: Vec<usize>,
    rank: Vec<usize>,
    size: Vec<usize>,
}

#[allow(dead_code)]
impl UnionFind {
    fn new(n: usize) -> UnionFind {
        let mut p = vec![0; n];
        for i in 0..n {
            p[i] = i;
        }
        return UnionFind {
            parent: p,
            rank: vec![0; n],
            size: vec![1; n],
        };
    }

    fn find(&mut self, x: usize) -> usize {
        if x == self.parent[x] {
            x
        } else {
            let p = self.parent[x];
            let pr = self.find(p);
            self.parent[x] = pr;
            pr
        }
    }

    fn same(&mut self, a: usize, b: usize) -> bool {
        self.find(a) == self.find(b)
    }

    fn unite(&mut self, a: usize, b: usize) {
        let a_root = self.find(a);
        let b_root = self.find(b);
        if a_root == b_root {
            return;
        }
        if self.rank[a_root] > self.rank[b_root] {
            self.parent[b_root] = a_root;
            self.size[a_root] += self.size[b_root];
        } else {
            self.parent[a_root] = b_root;
            self.size[b_root] += self.size[a_root];
            if self.rank[a_root] == self.rank[b_root] {
                self.rank[b_root] += 1;
            }
        }
    }

    fn get_size(&mut self, x: usize) -> usize {
        let root = self.find(x);
        self.size[root]
    }
}

const MOD_P: usize = 1000000007;

#[allow(dead_code)]
// fact(n) = n! mod p
fn fact(n: usize) -> usize {
    let mut acc = 1;
    for i in 1..n + 1 {
        acc = acc * i % MOD_P;
    }
    acc
}

#[allow(dead_code)]
fn mod_pow(b: usize, mut e: usize) -> usize {
    let mut base = b;
    let mut acc = 1;

    while e > 1 {
        if e % 2 == 1 {
            acc = acc * base % MOD_P;
        }
        e /= 2;
        base = base * base % MOD_P;
    }

    if e == 1 {
        acc = acc * base % MOD_P;
    }

    acc
}

#[allow(dead_code)]
fn comb(n: usize, r: usize) -> usize {
    // nCr = n! / (r! (n-r)!) = n! (r!)^(p-2) ((n-r)!)^(p-2)
    let x = ((n - r + 1)..(n + 1)).fold(1, |p, x| p * x % MOD_P);
    let y = mod_pow(fact(r), MOD_P - 2);
    x * y % MOD_P
}

#[derive(Clone, Copy, Debug)]
struct GF(usize);

impl std::ops::Add for GF {
    type Output = GF;
    fn add(self, rhs: GF) -> Self::Output {
        let mut d = self.0 + rhs.0;
        if d >= MOD_P {
            d -= MOD_P;
        }
        GF(d)
    }
}

impl std::ops::AddAssign for GF {
    fn add_assign(&mut self, rhs: GF) {
        *self = *self + rhs;
    }
}

impl std::ops::Sub for GF {
    type Output = GF;
    fn sub(self, rhs: GF) -> Self::Output {
        let mut d = self.0 + MOD_P - rhs.0;
        if d >= MOD_P {
            d -= MOD_P;
        }
        GF(d)
    }
}

impl std::ops::SubAssign for GF {
    fn sub_assign(&mut self, rhs: GF) {
        *self = *self - rhs;
    }
}

impl std::ops::Mul for GF {
    type Output = GF;
    fn mul(self, rhs: GF) -> Self::Output {
        let mut d = self.0 * rhs.0;
        d %= MOD_P;
        GF(d)
    }
}

impl std::ops::MulAssign for GF {
    fn mul_assign(&mut self, rhs: GF) {
        *self = *self * rhs;
    }
}

impl std::fmt::Display for GF {
    fn fmt<'a>(&self, f: &mut std::fmt::Formatter<'a>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

#[allow(dead_code)]
impl GF {
    pub fn new(n: usize) -> GF {
        GF(n % MOD_P)
    }
    pub fn zero() -> GF {
        GF(0)
    }
    pub fn one() -> GF {
        GF(1)
    }
    pub fn pow(self, mut e: usize) -> GF {
        let mut acc = GF::one();
        let mut b = self;
        while e > 1 {
            if e % 2 == 1 {
                acc *= b;
            }
            b *= b;
            e /= 2;
        }
        if e == 1 {
            acc *= b;
        }
        acc
    }
    pub fn fact(self) -> GF {
        let mut acc = GF::one();
        for i in 1..=self.0 {
            acc *= GF::new(i);
        }
        acc
    }
    pub fn inv(self) -> GF {
        self.pow(MOD_P - 2)
    }
    pub fn comb(n: GF, r: GF) -> GF {
        // nCr = n! / (r! (n-r)!) = n! (r!)^(p-2) ((n-r)!)^(p-2)
        let x = ((n.0 - r.0 + 1)..=n.0).fold(GF::one(), |p, x| p * GF(x));
        let y = r.fact().inv();
        x * y
    }
}

#[allow(dead_code)]
#[derive(Debug)]
struct MemComb {
    inv: Vec<GF>,
    fact: Vec<GF>,
    factinv: Vec<GF>,
}

#[allow(dead_code)]
impl MemComb {
    pub fn new(n: usize) -> MemComb {
        let mut inv = vec![GF::one(); n + 1];
        let mut fact = vec![GF::one(); n + 1];
        let mut factinv = vec![GF::one(); n + 1];

        for i in 2..=n {
            fact[i] = fact[i - 1] * GF(i);
        }

        factinv[n] = fact[n].inv();
        for i in (1..n).rev() {
            factinv[i] = factinv[i + 1] * GF(i + 1); // 1/n! = 1/(n+1)! * (n+1)
            inv[i] = factinv[i] * fact[i - 1]; // 1/n = 1/n! * (n-1)!
        }
        inv[n] = factinv[n] * fact[n - 1];

        MemComb { inv, fact, factinv }
    }
    pub fn comb(&self, n: usize, r: usize) -> GF {
        if n >= r {
            self.fact[n] * self.factinv[r] * self.factinv[n - r]
        } else {
            GF::zero()
        }
    }
}

#[allow(dead_code)]
fn gcd(a: usize, b: usize) -> usize {
    if b > a {
        gcd(b, a)
    } else if a % b == 0 {
        b
    } else {
        gcd(b, a % b)
    }
}

#[allow(dead_code)]
fn getline() -> String {
    let mut __ret = String::new();
    std::io::stdin().read_line(&mut __ret).ok();
    return __ret;
}

#[allow(unused_imports)]
use std::cmp::{max, min};

fn main() {
    input! {
        n: usize,
        a: [usize; n],
    }
    let s = a.iter().sum::<usize>();
    let mut cur = 0;
    for (_i, &x) in a.iter().enumerate() {
        if 2 * (x + cur) == s {
            println!("0");
            return;
        } else if 2 * (x + cur) > s {
            let d = min(s - 2 * cur, 2 * (cur + x) - s);
            println!("{}", d);
            break;
        } else {
            cur += x;
        }
    }

    // println!("{}", ans);
}