import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum N = 14;

void main() {
  try {
    for (; ; ) {
      const D = readInt();
      string A;
      A ~= readToken();
      A ~= readToken();
      
      const n = D + N + D;
      int ans;
      foreach (d; 0 .. D + 1) {
        foreach (i; 0 .. D + N + D - d + 1) {
          auto bs = new bool[D + N + D];
          foreach (j; 0 .. N) {
            bs[D + j] = (A[j] == 'o');
          }
          if (bs[i .. i + d].any) {
            continue;
          }
          bs[i .. i + d] = true;
          for (int x = 0, y; x < D + N + D; x = y) {
            for (y = x; y < D + N + D && bs[x] == bs[y]; ++y) {}
            if (bs[x]) {
              chmax(ans, y - x);
            }
          }
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}