/* -*- coding: utf-8 -*-
 *
 * 204.cc: No.204 ゴールデン・ウィーク(2) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_D = 14;
const char chs[] = {'x', 'o'};

/* typedef */

typedef vector<int> vi;

/* global variables */

/* subroutines */

/* main */

int main() {
  int d;
  string w0, w1;
  cin >> d >> w0 >> w1;

  string s = string(MAX_D, 'x') + w0 + w1 + string(MAX_D, 'x');
  int n = s.size();
  //cout << s << endl;

  vi ds[2];

  int pc = 0, k = 0;
  for (int i = 0; i < n; i++) {
    if (chs[pc] == s[i]) k++;
    else {
      if (k > 0) ds[pc].push_back(k);
      pc ^= 1;
      k = 1;
    }
  }
  if (k > 0) ds[pc].push_back(k);

  int maxl = d, dn = ds[1].size();

  for (int i = 0; i < dn; i++) {
    int l0 = min(ds[0][i], d) + ds[1][i];
    if (maxl < l0) maxl = l0;

    int l1;
    if (ds[0][i + 1] > d) l1 = ds[1][i] + d;
    else {
      l1 = ds[1][i] + ds[0][i + 1];
      if (i < dn - 1) l1 += ds[1][i + 1];
    }
    if (maxl < l1) maxl = l1;
  }

  printf("%d\n", maxl);
  return 0;
}