use std::io::*;

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

    let mut week = Vec::new();
    for i in 0..7 {
        week.push(s[i] == 'o');
    }
    for i in 0..7 {
        week.push(t[i] == 'o');
    }

    let mut ans = 0;
    for i in 0..14 {
        let mut cnt = 0;
        let mut u = week.clone();
        let mut j = i;
        while j < 14 {
            if !u[j] {
                if cnt == n {
                    break;
                }
                cnt += 1;
                u[j] = true;
            }
            j += 1
        }

        cnt = 0;
        for j in 0..14 {
            if u[j] {
                cnt += 1;
            } else {
                ans = std::cmp::max(ans, cnt);
                cnt = 0;
            }
        }
        ans = std::cmp::max(ans, cnt);
    }
    println!("{}", ans);
}