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

#include "bits/stdc++.h"

#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update

using namespace std;
using namespace __gnu_pbds;

#define pb push_back
#define F first
#define S second
#define f(i, a, b)  for(int i = a; i < b; i++)
#define all(a)  a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define sz(x) (int)(x).size()
#define mp(x,y) make_pair(x,y)
#define popCnt(x) (__builtin_popcountll(x))
//#define int ll

using ll = long long;
using ii = pair<int, int>;
using ull = unsigned long long;

const int N = 2e5+5, LG = 18, MOD = (119 << 23) + 1;
const long double PI = acos(-1);
const long double EPS = 1e-7;

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

int n, m;
vector<string> grid;
vector<vector<int>> cnt;

int ans = -1;
int mxSuffix[1000006];
int mxPrefix[1000006];
int nxt[1000006];
int v[1000006], ptr;
int solve(int n) {
    if(n < 5)
        return -1;
    for(int i = 0; i < n; i++) {
        mxPrefix[i] = v[i];
        if(i)mxPrefix[i] = max(mxPrefix[i], mxPrefix[i-1]);
    }

    for(int i = n - 1; i >= 0; --i) {
        mxSuffix[i] = v[i];
        if(i + 1 != n) {
            mxSuffix[i] = max(mxSuffix[i], mxSuffix[i + 1]);
        }
    }

    int ret = -1;
    for(int i = 2; i + 2 < n; i++) {

        for(int j = max(2,int(ans-n)/3+1); j <= v[i]; j++) {
            int lo = 0, hi = i - 2;
            while(lo < hi) {
                int md = lo + (hi-lo) / 2;
                if(mxPrefix[md] >= j)
                    hi = md;
                else
                    lo = md + 1;
            }
            int L = lo;
            lo = i + 2, hi = n - 1;
            while(lo < hi) {
                int md = lo + (hi - lo + 1) / 2;
                if(mxSuffix[md] >= j)
                    lo = md;
                else
                    hi = md - 1;
            }
            int R = lo;
            if(v[L] >= j && v[R] >= j) {
                ret = max(ret, (R-L+1) + (j-1) * 3);
            }   else break;
        }
    }

    return ret;
}
void doWork() {
    cin >> n >> m;
    grid.resize(n + 1);
    for(int i = 1; i <= n; i++) {
        cin >> grid[i];
        grid[i] = "#" + grid[i];
    }

    for(int col = m; col >= 1; --col) {
        for(int i = 1; i <= n; i++) {
            if(grid[i][col] == '#') nxt[i]  = 0;
            else nxt[i] += 1;
        }
        for(int i = 1, j = 1; i <= n; i = j) {
            if(grid[i][col] == '#')j = i + 1;
            else {
                ptr = 0;
                for(;j <= n && grid[j][col] == '.'; j++)
                    v[ptr++] = nxt[j];
                ans = max(ans, solve(ptr));
            }
        }
    }

    cout << ans << '\n';

}
int32_t main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#endif // ONLINE_JUDGE

    int t = 1;
//    cin >> t;
    while (t--) {
        doWork();
    }
    return 0;
}

///Look at my code ya codeomk