use std::io;


fn read_line() -> String {
    let mut line = String::new();

    io::stdin().read_line(&mut line)
        .expect("Failed to read line");
    return line;
}
fn to_i(s: &str) -> i64 {
    return s.trim().parse()
        .expect("Please type a number!");
}
fn read_nums() -> Vec<i64>
{
    let line = read_line();
    let items: Vec<&str> = line.split(' ').collect();

    let mut nums: Vec<i64> = Vec::new();

    for item in items {
        nums.push(to_i(item));
    }
    return nums;
}

fn calc(n: i64, s: &Vec<char>,  flag: bool) -> i64 {
    let mut count = 0;
    let mut prev = flag;
    for i in 0..n {
        let c  = s[i as usize];
        if i == 0 {
            if c == '#' {
                if flag {
                    prev = true;
                }else {
                    prev = false;
                    count += 1;
                }
            } else {
                if flag {
                    prev = true;
                    count += 1;
                }else {
                    prev = false;
                }
            }
        } else {
            if c == '#' {
                if prev {
                    prev = true;
                } else {
                    prev = false;
                }
            } else {
                if prev {
                    prev = true;
                    count += 1;
                } else {
                    prev = false;
                }
            }
        }
        
        
    }
    count
}
fn main() {
    let n: i64 = to_i( &read_line() );
    let s: Vec<char> = read_line().chars().collect();

    let c1 = calc(n, &s, false);
    let c2 = calc(n, &s, true);

    let mut ret = 0;
    if c1<c2 {
        ret = c1;
    } else {
        ret = c2;
    }

    print!("{}", ret);
}   