fn main() {
    let vec: Vec<usize> = read_vec();
    let index = vec[1];

    let text: String = read();
    let mut chars: Vec<char> = text.chars().collect();
    
    let mut ans = hoge(index, chars.clone());
    
    if ans == 0 {
        chars.reverse();
        ans = vec[0] - hoge_rev(vec[0] - index + 1, chars) + 1;
    }

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

fn hoge(index: usize, chars: Vec<char>) -> usize {
    let mut counter = 0;

    for i in 0..index {
        match chars[i] {
            '(' => { counter += 1; },
            ')' => { counter -= 1; },
            _   => {},
        }
    }

    let registor = counter;

    for i in index..chars.len() {
        match chars[i] {
            '(' => { counter += 1; },
            ')' => { counter -= 1; },
            _   => {},
        }

        if counter == registor - 1 {
            return i + 1;
        }
    }
    return 0;
}

fn hoge_rev(index: usize, chars: Vec<char>) -> usize {
    let mut counter = 0;

    for i in 0..index {
        match chars[i] {
            ')' => { counter += 1; },
            '(' => { counter -= 1; },
            _   => {},
        }
    }

    let registor = counter;

    for i in index..chars.len() {
        match chars[i] {
            ')' => { counter += 1; },
            '(' => { counter -= 1; },
            _   => {},
        }

        if counter == registor - 1 {
            return i + 1;
        }
    }
    return 0;
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().split_whitespace()
        .map(|e| e.parse().ok().unwrap()).collect()
}