#include <bits/stdc++.h>
using namespace std;
const int N = 505;
int cnt[N * N], par[N][N], sum[N][N], sz[N * N];
char grid[N][N];
int n, k;
int cur = 0;
void change(int id, int add) {
  if (id == 0) return;
  if (cnt[id]) cur -= sz[id];
  cnt[id] += add;
  if (cnt[id]) cur += sz[id];
}
void paint(int r, int c, int col) {
  if (r < 1 || c < 1 || r > n || c > n) return;
  if (grid[r][c] != '.') return;
  if (par[r][c] != 0) return;
  par[r][c] = col;
  ++sz[col];
  paint(r - 1, c, col);
  paint(r + 1, c, col);
  paint(r, c - 1, col);
  paint(r, c + 1, col);
}
int inside(int r, int c) {
  return sum[r + k - 1][c + k - 1] - sum[r - 1][c + k - 1] -
         sum[r + k - 1][c - 1] + sum[r - 1][c - 1];
}
int main() {
  cin >> n >> k;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j) scanf(" %c", &grid[i][j]);
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= n; ++j)
      if (grid[i][j] == '.') {
        if (par[i][j] == 0) {
          paint(i, j, i * n + j);
        }
      }
  for (int i = 1; i < N; ++i)
    for (int j = 1; j < N; ++j)
      sum[i][j] = sum[i - 1][j] + sum[i][j - 1] - sum[i - 1][j - 1] +
                  (grid[i][j] != '.');
  int ans = 0;
  for (int i = 1; i <= n - k + 1; ++i) {
    memset(cnt, 0, sizeof(cnt));
    cur = 0;
    for (int r = i - 1; r <= i + k; ++r)
      for (int c = 0; c <= k + 1; ++c) change(par[r][c], 1);
    change(par[i - 1][k + 1], -1);
    change(par[i + k][k + 1], -1);
    ans = max(ans, cur + inside(i, 1));
    for (int j = 2; j <= n - k + 1; ++j) {
      for (int r = i - 1; r <= i + k; ++r) {
        change(par[r][j + k], 1);
      }
      change(par[i - 1][j + k - 1], +1);
      change(par[i + k][j + k - 1], +1);
      change(par[i - 1][j - 2], +1);
      change(par[i + k][j - 2], +1);
      for (int r = i - 1; r <= i + k; ++r) {
        change(par[r][j - 2], -1);
      }
      change(par[i - 1][j + k], -1);
      change(par[i + k][j + k], -1);
      change(par[i - 1][j - 1], -1);
      change(par[i + k][j - 1], -1);
      ans = max(ans, cur + inside(i, j));
    }
  }
  cout << ans << '\n';
}
