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

const int N = 50;

char tiles[N + 5][N + 5];
bool visited[N + 5][N + 5];

int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};

bool in_range(int x, int y, int rows, int cols) {
  return x >= 0 && x < rows && y >= 0 && y < cols;
}

int dfs(int x, int y, int rows, int cols) {
  if (!in_range(x, y, rows, cols) || visited[x][y] || tiles[x][y] == 'B') {
    return 0;
  }

  visited[x][y] = true;
  int size = 1;

  for (int i = 0; i < 4; ++i) {
    int px = x + dx[i];
    int py = y + dy[i];

    size += dfs(px, py, rows, cols);
  }

  return size;
}

int find_largest_area(int rows, int cols) {
  int max_size = 0;

  for (int i = 0; i < rows; i++) {
    for (int j = 0; j < cols; j++) {
      if (!visited[i][j] && tiles[i][j] == 'A') {
        int size = dfs(i, j, rows, cols);
        max_size = max(max_size, size);
      }
    }
  }

  return max_size;
}

int main() {
  int n;
  cin >> n;
  for (int x = 0; x < n; x++)
    for (int y = 0; y < n; y++)
      cin >> tiles[x][y];
  int max_chunk = 0;
  for (int x = 0; x < n; x++) {
    for (int y = 0; y < n; y++) {
      if (tiles[x][y] == 'A')
        continue;
      tiles[x][y] = 'A';
      memset(visited, 0, sizeof visited);
      max_chunk = max(max_chunk, find_largest_area(n, n));
      tiles[x][y] = 'B';
    }
  }
  cout << max_chunk << endl;
}