#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

ll count_o(string s){
    ll L = s.size();
    
    ll start = -1;
    FOR(i, 0, L){
        if(s[i]=='o'){
            start = i;
            break;
        }
    }
    if(start==-1) return 0;

    ll count = 0;
    FOR(i, start, L){
        if(s[i]=='o'){
            count++;
        }else{
            break;
        }
    }
    return count;
}

string rip_off_outer_o(string s){
    ll L = s.size();
    ll start = -1;
    FOR(i, 0, L){
        if(s[i]=='o'){
            start = i;
            break;
        }
    }

    ll end = -1;
    for(int i=L-1; i>=0; i--){
        if(s[i]=='o'){
            end = i;
            break;
        }
    }

    stringstream ss;
    FOR(i, start, end+1){
        ss << s[i];
    }
    return ss.str();
}

ll max_o_len(string s){
    ll L = s.size();
    ll max_len = 0;
    FOR(i, 0, L){
        if(s[i]=='o'){
            ll len = 0;
            FOR(j, i, L){
                if(s[j]=='o'){
                    len++;
                }else{
                    break;
                }
            }
            max_len = max(max_len, len);
        }
    }
    return max_len;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll D;
    cin >> D;

    string s;
    cin >> s;

    string temp;
    cin >> temp;

    s = s + temp;
    ll L = s.size();
    string t = s;
    reverse(ALL(t));

    ll left = count_o(s);
    ll right = count_o(t);

    // o??????oなる文字列
    string u = rip_off_outer_o(s);

    ll center = 0;
    if(u.size()>0){
        FOR(i, 0, u.size()){
            if(u[i]=='x'){
                // そこからKのばす
                string v = u;
                ll count = 0;
                FOR(j, i, v.size()){
                    if(v[j]=='x'){
                        v[j] = 'o';
                        count++;
                        if(count==D) break;
                    }else{
                        break;
                    }
                }
                // vが書き換えられた
                ll len = max_o_len(v);
                center = max(center, len);
            }
        }
    }

    left += D;
    right += D;
    ll ans = max(left, right);
    ans = max(ans, center);
    p(ans);
    
    return 0;
}