#include <queue>
#include <algorithm>
#include <vector>
#include <iostream>
#include <numeric>
#include <tuple>
using namespace std;
typedef long long int ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define ALL(container) (container).begin(), (container).end()

int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    string f;
    string s;
    cin >> f;
    cin >> s;
    const string m = "xxxxxxxxxxxxxx" + f + s + "xxxxxxxxxxxxxx";
    int maxValue = 0;
    {
        int current = 0;
        for(int j = 0;j < m.length();j++)
        {
            if(m[j] == 'o')
            {
                current++;
                maxValue = max(maxValue, current);
            }
            else
            {
                current = 0;
            }
        }
    }
    for(int i = 0; i < m.length();i++)
    {
        if(m[i] == 'o')
        {
            continue;
        }
        int current = 0;
        bool seq = true;
        for(int j = 0;j < m.length();j++)
        {
            if(j >= i && j < i + n && seq)
            {
                if(m[j] == 'o')
                {
                    seq = false;
                }
                current++;
                maxValue = max(maxValue, current);
            }
            else if(m[j] == 'o')
            {
                current++;
                maxValue = max(maxValue, current);
            }
            else
            {
                current = 0;
            }
        }
    }
    cout << maxValue << endl;
    return 0;
}