#include <algorithm>
#include <vector>
#include <cfloat>
#include <string>
#include <cmath>
#include <set>
#include <cstdlib>
#include <map>
#include <ctime>
#include <iomanip>
#include <functional>
#include <deque>
#include <iostream>
#include <cstring>
#include <queue>
#include <cstdio>
#include <stack>
#include <climits>
#include <sys/time.h>
#include <cctype>

using namespace std;

typedef long long ll;

int main() {
  int d;
  cin >> d;
  string s, t;
  cin >> s;
  cin >> t;
  s += t;
  t = s;

  int ans = -1, cnt = 0;
  for (int i = 0; i < s.size()-1; i++) {
    if (s[i+1] != 'o') {
      ans = i+1+d;
      break;
    }
  }
  if (ans == -1) {
    ans = s.size()+d;
  }

  for (int p = 0; p < s.size()-d+1; p++) {
    for (int i = 0; i < d; i++) {
      s[p+i] = 'o';
    }
    cnt = 0;
    for (int i = 0; i < s.size(); i++) {
      if (s[i] == 'o') {
	cnt++;
      }else {
	ans = max(ans, cnt);
	cnt = 0;
      }
    }
    ans = max(ans, cnt);
    s = t;
  }

  std::cout << ans << std::endl;
}