#include <iostream>
#include <vector>
#include <fstream>

int m = 0;
int r = 0;

bool tryMoveRight(std::vector<std::vector<int>>& map, int x, int y, int color) {
  for (int i = 0; i < r; ++i) {
    if (map[y - i][x] == -1) {
      return false;
    }
  }
  for (int i = 0; i < r; ++i) {
    map[y - i][x] = color;
  }
  return true;
}

bool tryMoveDown(std::vector<std::vector<int>>& map, int x, int y, int color) {
  for (int i = 0; i < r; ++i) {
    if (map[y][x - i] == -1) {
      return false;
    }
  }
  for (int i = 0; i < r; ++i) {
    map[y][x - i] = color;
  }
  return true;
}

void findPath(std::vector<std::vector<int>>& map, int x, int y, int color) {
  if (tryMoveRight(map, x + 1, y, color + 1)) {
    findPath(map, x + 1, y, color + 1);
  }
  if (tryMoveDown(map, x, y + 1, color + 1)) {
    findPath(map, x, y + 1, color + 1);
  }
}

int main() {
  std::ifstream input("input.txt");
  if (!input.good()) {
    std::cout << "File error: input.txt\n";
    return 1;
  }
  input >> m >> r;
  std::vector<std::vector<int>> map(m + 2);
  for (int i = 0; i < m + 2; ++i) {
    map[i].resize(m + 2);
  }
  for (int i = 0; i < m + 2; ++i) {
    map[0][i] = -1;
    map[i][0] = -1;
    map[m + 1][i] = -1;
    map[i][m + 1] = -1;
  }
  for (int i = 1; i < m + 1; ++i) {
    char c = 0;
    for (int j = 1; j < m + 1; ++j) {
      input >> c;
      map[i][j] = c == '.' ? 0 : -1;
    }
  }
  input.close();

  findPath(map, r, r, 0);

  std::ofstream output("output.txt");
  if (!output.good()) {
    std::cout << "File error: output.txt\n";
    return 1;
  }
  if (map[m][m] == 0) {
    output << "No";
  } else {
    output << map[m][m];
  }

  return 0;
}