fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let s = s.trim().chars().collect::<Vec<char>>();

    let mut cnts = vec![vec![0usize; 3]; 3];
    for i in 0..s.len() {
        let c = s[i];
        if c == 'c' {
            cnts[0][i%3] += 1;
        } else if c == 'o' {
            cnts[1][i%3] += 1;
        } else if c == 'n' {
            cnts[2][i%3] += 1;
        }
    }
    println!("{}", (0..3).map(|i| cnts[0][i].min(cnts[1][(i+1)%3]).min(cnts[2][(i+2)%3])).sum::<usize>());
}