#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <utility>
#include <string>
#include <algorithm>
#include <map>
#include <vector>
#include <climits>
#include <numeric>
#include<stdio.h>
#include <queue>
#include <iomanip>
#include <float.h>
#include <set>
#include<functional>
#include <stack>
#include <time.h>
#include <climits>
#include <bitset>
#include <fstream>
using namespace std;
typedef pair<int, int>p;
long long gcd(long long a, long long b) {
	if (b == 0) return a;
	return gcd(b, a % b);
}
vector<long long> divisor(long long n) {
	vector< long long> ret;
	for (long long i = 1; i * i <= n; i++) {
		if (n % i == 0) {
			ret.push_back(i);
			if (i * i != n) ret.push_back(n / i);
		}
	}
	sort(begin(ret), end(ret));
	return (ret);
}
long long mod = 1e9 + 7;
struct LazySegmentTree {
private:
	int n;
	vector<int> node, lazy;
	vector<bool> lazyFlag;

public:
	LazySegmentTree(vector<int> v) {
		int sz = (int)v.size();
		n = 1; while (n < sz) n *= 2;
		node.resize(2 * n - 1);
		lazy.resize(2 * n - 1, INT_MAX);
		lazyFlag.resize(2 * n - 1, false);

		for (int i = 0; i<sz; i++) node[i + n - 1] = v[i];
		for (int i = n - 2; i >= 0; i--) node[i] = min(node[i * 2 + 1], node[i * 2 + 2]);
	}

	void lazyEvaluate(int k, int l, int r) {
		if (lazyFlag[k]) {
			node[k] = lazy[k];
			if (r - l > 1) {
				lazy[k * 2 + 1] = lazy[k * 2 + 2] = lazy[k];
				lazyFlag[k * 2 + 1] = lazyFlag[k * 2 + 2] = true;
			}
			lazyFlag[k] = false;
		}
	}

	void update(int a, int b, int x, int k = 0, int l = 0, int r = -1) {
		if (r < 0) r = n;
		lazyEvaluate(k, l, r);
		if (b <= l || r <= a) return;
		if (a <= l && r <= b) {
			lazy[k] = x;
			lazyFlag[k] = true;
			lazyEvaluate(k, l, r);
		}
		else {
			update(a, b, x, 2 * k + 1, l, (l + r) / 2);
			update(a, b, x, 2 * k + 2, (l + r) / 2, r);
			node[k] = min(node[2 * k + 1], node[2 * k + 2]);
		}
	}

	int find(int a, int b, int k = 0, int l = 0, int r = -1) {
		if (r < 0) r = n;
		lazyEvaluate(k, l, r);
		if (b <= l || r <= a) return INT_MAX;
		if (a <= l && r <= b) return node[k];
		int vl = find(a, b, 2 * k + 1, l, (l + r) / 2);
		int vr = find(a, b, 2 * k + 2, (l + r) / 2, r);
		return min(vl, vr);
	}
};
signed main()
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(16);
	int h, w;
	cin >> h >> w;
	int a[2003][2003];
	int num[2003][2003];
	int num2[2003][2003];
	string s;
	for (int i = 0; i < h; i++) {
		cin >> s;
		for (int j = 0; j < w; j++) {
			if (s[j] == '#')a[i][j] = 1;
			else a[i][j] = 0;
		}
	}
	for (int i = 0; i < h; i++) {
		int number = 0;
		int index = 0;
		for (int j = 0; j < w; j++) {
			if (a[i][j] == 0)number += 1;
			if (j == w-1 || a[i][j] == 1) {
				for (int k = index; k <= j; k++) {
					num[i][k] = number;
				}
				number = 0;
				index = j+1;
			}
		}
		for (int j = 0; j < w; j++) {
			if (a[i][j] == 1)num[i][j] = 0;
		}
	}
	for (int j = 0; j < w; j++) {
		int number = 0;
		int index = 0;
		for (int i = 0; i < h; i++) {
			if (a[i][j] == 0)number += 1;
			if (i == h-1 || a[i][j] == 1) {
				for (int k = index; k <= i; k++) {
					num2[k][j] = number;
				}
				number = 0;
				index = i+1;
			}
		}
		for (int i = 0; i < h; i++) {
			if (a[i][j] == 1)num2[i][j] = 0;
		}
	}
	int ans = 0;
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			if(a[i][j]==0)
			ans = max(ans, num[i][j] + num2[i][j]);
		}
	}
	cout << ans-1;
}

Measured memory_bytes: 47232