// (；ω；)＜柔軟な発送が足りなかった…
#include <bits/stdc++.h>
using namespace std;

class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};

int main(void) {
  int d; scanf("%d", &d);
  string s1, s2; cin >> s1 >> s2;
  string s;
  for(int i : range(14)) { s += "x"; }
  s += s1 + s2;
  for(int i : range(14)) { s += "x"; }
  int ha = 0;
  for(int i : range(s.size()-d+1)) {
    string cp = s;
    for(int j : range(i, i+d)) {
      if(cp[j] == 'x') { cp[j] = 'o'; }
      else { break; }
    }
    int cnt = 0;
    for(int k : range(s.size())) {
      if(cp[k] == 'o') { cnt += 1; }
      else { cnt = 0; }
      ha = max(ha, cnt);
    }
  }
  printf("%d\n", ha);
  return 0;
}