#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)
typedef long long ll;

int main(){
  int D;
  cin >> D;
  string s,ss;
  cin >> s >> ss;
  s += ss;
  s = "xxxxxxxxxxxxxx" + s + "xxxxxxxxxxxxxx";
  int ans = 0;
  FOR (i,0,42-D+1) {
    int con = 0;
    int MAX = 0;
    ss = s;
    FOR (j,0,D) {
      if (ss[j+i] == 'o') break;
      ss[j+i] = 'o';
    }
    FOR (j,0,42) {
      if (ss[j] == 'o') {
        con++;
      } else {
        MAX = max(MAX, con);
        con = 0;
      }
    }
    MAX = max(MAX, con);
    ans = max(ans, MAX);
  }
  cout << ans << endl;
  return 0;
}