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()
}

pub fn main() {
    let N: usize = read();
    let S: String = read();
    let mut w_counter = 0;
    let mut start = false;
    for c in S.chars() {
        if c == '.' {
            if !start {
                continue;
            }
            w_counter += 1;
        } else {
            start = true;
        }
    }

    let mut b_counter = 0;
    start = false;
    for c in S.chars().rev() {
        if c == '#' {
            if !start {
                continue;
            }
            b_counter += 1;
        } else {
            start = true;
        }
    }
    println!("{}", ::std::cmp::min(w_counter, b_counter));
}