import java.util.*;

public class Exercise112{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int d = sc.nextInt();
    String plus = "xxxxxxxxxxxxxx";
    String weeks = plus + sc.next() + sc.next() + plus;
    char[] wa = weeks.toCharArray();
    int max = 0;
    for(int i = 0; i < wa.length; i++){
      if(wa[i] == 'x'){
        char[] wd = Arrays.copyOf(wa, wa.length);
        for(int j = 0; j < d && i + j < wd.length; j++){
          if(wd[i + j] == 'o'){
            break;
          }
          wd[i + j] = 'o';
        }
        int oCount = 0;
        for(char charInWd: wd){
          if(charInWd == 'o'){
            oCount++;
            max = Math.max(max, oCount);
          }else{
            oCount = 0;
          }
        }
      }
    }
    System.out.println(max);
  }
}