use proconio::marker::*;
use proconio::*;
use std::collections::*;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;
type Heap<T> = BinaryHeap<T>;

const MOD: u64 = 998_244_353;

fn main() {
    input! {
        n: usize,
        mut s: Bytes,
        r: usize,
        m: usize,
    }

    if n & 1 == 1 {
        println!("-1");
        return;
    }

    let mut ans = 0usize;

    let x = s.iter().filter(|c| **c == b'(').count();
    if x * 2 > n {
        let mut d = x - n / 2;
        for c in s.iter_mut().rev() {
            if *c == b'(' {
                *c == b')';
                ans += 1;
                d -= 1;
                if d == 0 {
                    break;
                }
            }
        }
    }
    if x * 2 < n {
        let mut d = n / 2 - x;
        for c in s.iter_mut() {
            if *c == b')' {
                *c == b'(';
                ans += 1;
                d -= 1;
                if d == 0 {
                    break;
                }
            }
        }
    }

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