#include <iostream>
#include <algorithm>
using namespace std;

int main(){
  int d;
  cin >> d;
  string a, b;
  cin >> a >> b;
  string str = a + b;

  int count, result;
  for(int i = 1; i <= 14; i++){
    for(int j = 0; j < 15 - i; j++){
      count = 0;
      for(int k = 0; k < i; k++){
        if(str[j + k] == 'x')
          count++;
      }
      if(count <= d){
        result = i;
        break;
      }
    }
  }
  cout << result << endl;
}