#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t, n, m, a, b, c, q, k, d, x;
  cin >> n >> m;
  vector<vector<int>> mat(n + 1, vector<int>(m + 1)),
      ans(n + 1, vector<int>(m + 1));
  char ch;
  for (int i = 1; i < n + 1; i++) {
    for (int j = 1; j < m + 1; j++) {
      cin >> ch;
      mat[i][j] = ch - '0';
      ans[i][j] = ans[i - 1][j] + ans[i][j - 1] - ans[i - 1][j - 1] + mat[i][j];
    }
  }
  a = 0;
  for (int i = 1; i < n + 1; i++) {
    for (int j = 1; j < m + 1; j++) {
      for (int i_ = i; i_ < n + 1; i_++) {
        for (int j_ = j; j_ < m + 1; j_++) {
          if (ans[i_][j_] - ans[i - 1][j_] - ans[i_][j - 1] +
                  ans[i - 1][j - 1] ==
              0) {
            a = max(a, 2 * (i_ - i + 1 + j_ - j + 1));
          }
        }
      }
    }
  }
  cout << a << "\n";
  return 0;
}
