#include <iostream>
#include <iomanip>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <stack>
#include <queue>
#include <bitset>
#include <numeric>
#include <random>

/* (=＾o＾=) */
#define int ll

/* macro */
#define FOR(i, b, e) for(ll i = (ll)(b); i < (ll)(e); ++i)
#define RFOR(i, b, e) for(ll i = (ll)(e-1); i >= (ll)(b); --i)
#define REP(i, n) FOR(i, 0, n)
#define RREP(i, n) RFOR(i, 0, n)
#define REPC(x,c) for(const auto& x:(c))
#define REPI2(it,b,e) for(auto it = (b); it != (e); ++it)
#define REPI(it,c) REPI2(it, (c).begin(), (c).end())
#define RREPI(it,c) REPI2(it, (c).rbegin(), (c).rend())
#define REPI_ERACE2(it, b, e) for(auto it = (b); it != (e);)
#define REPI_ERACE(it, c) REPI_ERACE2(it, (c).begin(), (c).end())
#define ALL(x) (x).begin(),(x).end()
#define cauto const auto&
/* macro func */
#define SORT(x) do{sort(ALL(x));}while(false)
#define RSORT(x) do{sort((x).rbegin(),(x).rend());}while(false)
#define UNIQUE(v) do{v.erase( unique(v.begin(), v.end()), v.end() );}while(false)
#define MAX(x,y) do{x = std::max(x,y);}while(false)
#define MIN(x,y) do{x = std::min(x,y);}while(false)
#define BR do{cout<<"\n";}while(false)
#define dump(...) do{ auto __DUMP_NAME_LIST__ = split(#__VA_ARGS__,','); print(__DUMP_NAME_LIST__, __VA_ARGS__);BR;}while(false)

/* type define */
using ll = long long;
using PAIR = std::pair<ll, ll>;
using VS = std::vector<std::string>;
using VL = std::vector<long long>;
using VVL = std::vector<VL>;
using VVVL = std::vector<VVL>;
using VD = std::vector<double>;

/* using std */
using std::cout;
constexpr char endl = '\n';
using std::cin;
using std::sort;
using std::pair;
using std::string;
using std::stack;
using std::queue;
using std::vector;
using std::list;
using std::map;
using std::unordered_map;
using std::multimap;
using std::unordered_multimap;
using std::set;
using std::unordered_set;
using std::unordered_multiset;
using std::multiset;
using std::bitset;
using std::priority_queue;

/* constant value */
constexpr ll MOD = 1000000007;
//constexpr ll MOD = 998244353;

/* Initial processing  */
struct Preprocessing { Preprocessing() { std::cin.tie(0); std::ios::sync_with_stdio(0); }; }_Preprocessing;

/* define hash */
namespace std { template <>	class hash<std::pair<ll, ll>> { public:	size_t operator()(const std::pair<ll, ll>& x) const { return hash<ll>()(1000000000 * x.first + x.second); } }; }

/* input output */
template<class T> std::istream& operator >> (std::istream& is, vector<T>& vec) { for (T& x : vec) is >> x; return is; }
template<class S, class T>std::ostream& operator<<(std::ostream& os, const std::pair<S, T>& p) { os << "(" << p.first << ", " << p.second << ")"; return os; }

/* for dump function */
inline std::list<std::string> split(std::string str, char del) { std::list<std::string> sList; string s = ""; for (const auto& c : str) { if (c == del) { sList.emplace_back(s); s = ""; } else { if (c != ' ' || del == ' ') { s += c; } } }sList.emplace_back(s);	return sList; }
template<class T>struct has_begin { private:	template <class U>	static auto check(U x) -> decltype(x.begin(), std::true_type{});	static std::false_type check(...); public:	static bool const value = decltype(check(std::declval<T>()))::value; };
inline void print(std::list<std::string>& str); template<class Primitive, class... Tail, std::enable_if_t<!has_begin<Primitive>::value, std::nullptr_t> = nullptr>inline void print(std::list<std::string> & str, const Primitive & x, const Tail & ... tail); template<class Container, class... Tail>inline auto print(std::list<std::string>& str, const Container& c, const Tail& ... tail) -> decltype(c.begin()); template<class... Tail>inline void print(std::list<std::string>& str, const std::string& s, const Tail& ... tail);
template<class Container>inline auto printSingle(const Container& c) ->decltype(c.begin()) { for (const auto& x : c) { std::cout << x << " "; }std::cout << "\n"; return c.begin(); }
template<class Primitive, std::enable_if_t<!has_begin<Primitive>::value, std::nullptr_t> = nullptr>inline void printSingle(const Primitive & x) { std::cout << x << " "; }
inline void print(std::list<std::string>& str) {}
template<class Primitive, class... Tail, std::enable_if_t<!has_begin<Primitive>::value, std::nullptr_t>>inline void print(std::list<std::string>& str, const Primitive& x, const Tail& ... tail) { std::cout << *str.begin() << ":" << x << " "; if (sizeof...(tail) > 0) { std::cout << "\n"; str.pop_front(); print(str, tail...); } }
template<class Container, class... Tail>inline auto print(std::list<std::string>& str, const Container& c, const Tail& ... tail) ->decltype(c.begin()) { std::cout << "-- " << *str.begin() << " --\n"; for (const auto& x : c) { printSingle(x); BR; }std::cout << "\n"; str.pop_front();	print(str, tail...); return c.begin(); }
template<class... Tail>inline void print(std::list<std::string>& str, const std::string& s, const Tail& ... tail) { std::cout << *str.begin() << ":" << s << "\n"; str.pop_front();	print(str, tail...); }

//=============================================================================================
/**
 *	UnionFind木を構成する
 *	nodeの深さ，木のサイズを取得可能
 */
class UnionFind {
	std::vector<ll> m_root;
	std::vector<ll> m_depth;
	std::vector<ll> m_size;
public:
	UnionFind(ll size_) : m_root(size_), m_depth(size_, 0), m_size(size_, 1) {
		std::iota(m_root.begin(), m_root.end(), 0);
	}
	void unite(ll x, ll y) {
		x = root(x);
		y = root(y);
		if (x == y) return;
		ll t = size(x) + size(y);
		m_size[x] = m_size[y] = t;
		if (m_depth[x] < m_depth[y]) m_root[x] = y;
		else m_root[y] = x;
		if (m_depth[x] == m_depth[y]) ++m_depth[x];
	}
	bool isSame(ll x, ll y) {
		return root(x) == root(y);
	}
	ll root(ll x) {
		if (m_root[x] == x) return x;
		return m_root[x] = root(m_root[x]);
	}
	ll size(ll x) {
		if (m_root[x] == x) return m_size[x];
		return size(m_root[x] = root(m_root[x]));
	}
};

signed main() {
	ll h, w;
	cin >> h >> w;

	VS mat(h);
	cin >> mat;

	auto row = vector<UnionFind>(h, UnionFind(w));
	REP(i, h) REP(j, w - 1) {
		if (mat[i][j] == '.' && mat[i][j + 1] == '.') {
			row[i].unite(j, j + 1);
		}
	}
	auto col = vector<UnionFind>(w, UnionFind(h));
	REP(i, h - 1) REP(j, w) {
		if (mat[i][j] == '.' && mat[i + 1][j] == '.') {
			col[j].unite(i, i + 1);
		}
	}
	ll ans = 0;
	REP(i, h)REP(j, w) {
		if (mat[i][j] == '#') { continue; }
		MAX(ans, row[i].size(j) + col[j].size(i) - 1);
	}
	cout << ans << endl;
}


Measured memory_bytes: 194560