#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ld long double


const int N = 1e6 + 5, mod = 998244353;

int n, m, cnt[N], ans = -1;
string grid[N];

void solve(vector<int> &nums) {
    // cout << "Size = " << nums.size() << '\n';
    // for (auto &i : nums) 
    //     cout << i << ' ';
    // cout << endl;
    vector<int> prefixMax(nums.size()), suffixMax(nums.size());
    for (int i = 0; i < nums.size(); ++i) {
        prefixMax[i] = (i ? max(nums[i], prefixMax[i - 1]) : nums[i]);
    }
    for (int i = int(nums.size()) - 1; i >= 0; --i) {
        suffixMax[i] = (i + 1 != nums.size() ? max(nums[i], suffixMax[i + 1]) : nums[i]);
    }
    for (int i = 2; i + 2 < nums.size(); ++i) {
        for (int len = max(1, (ans - int(nums.size())) / 3 + 1); len <= nums[i]; ++len) {
            int lw = 0, hi = i - 2;
            while (lw < hi) {
                int mid = lw + hi >> 1;
                if (prefixMax[mid] < len) {
                    lw = mid + 1;
                } else {
                    hi = mid;
                }
            }
            int st = hi;
            lw = i + 2, hi = int(nums.size()) - 1;
            while (lw < hi) {
                int mid = (lw + hi + 1) >> 1;
                if (suffixMax[mid] < len) {
                    hi = mid - 1;
                } else {
                    lw = mid;
                }
            }
            int en = lw;
            int cur_ans = (en - st + 1) + 3 * len; 
            // cout << st << ' ' << en << ' ' << cur_ans << '\n';
            // cout << len << ' ' << st << ' ' << nums[st] << ' ' << en << ' ' << nums[en] << '\n';
            if (min(nums[st], nums[en]) < len) {
                break;
            }
            ans = max(ans, cur_ans);
        }
    }
}
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> m;
    for (int i = 0; i < n; ++i) {
        cin >> grid[i];
    }
    for (int j = m - 1; j >= 0; --j) {
        // cout << "j = " << j << '\n'; 
        for (int i = 0; i < n; ++i) {
            cnt[i] = (grid[i][j] == '#' ? 0 : cnt[i] + 1);
        }
        vector<int> nums;
        for (int i = 0; i < n; ++i) {
            if (grid[i][j] == '#') {
                if (nums.size()) {
                    solve(nums);
                    nums.clear();   
                }
            } else {
                nums.push_back(cnt[i] - 1);
            }
        }
        if (nums.size()) {
            solve(nums);
        }
    }
    cout << ans << '\n';
    return 0;
}