#include <bits/stdc++.h>
#ifdef HIRO
#define d(f_, ...) printf((f_), ##__VA_ARGS__)
#else
#define d(f_, ...)
#endif

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<long long, long long> pllll;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector< pair<int, int> > vii;
typedef vector< pair<long long, long long> > vllll;
typedef map<int, int> mii;
typedef map<long long, long long> mllll;
typedef queue<int> qi;
typedef queue< pair<int, int> > qp;
#define mp make_pair
#define pi 3.14159265358979323846
#define MAX max_element
#define MIN min_element
#define all(v) v.begin(), v.end()
#define gt(T) greater<T>()
#define sum(v) accumulate(v.begin(), v.end(), 0ll)
#define uni(v) do{ \
  sort(v.begin(), v.end()); \
  decltype(v)::iterator result = unique(v.begin(), v.end()); \
  v.erase(result, v.end()); \
}while(0)
#define fi(init, n) for(int i = init; i < n; ++i)
#define fj(init, n) for(int j = init; j < n; ++j)
#define fk(init, n) for(int k = init; k < n; ++k)
#define zero(x) memset(x, 0, sizeof(x))
#define negative(x) memset(x, ~0, sizeof(x))
#define bitsum(x) __builtin_popcount(x)
const ll MOD = 1e9 + 7;
const int INF = 1e9;
const int di[] = { 0, 1, 0, -1 };
const int dj[] = { 1, 0, -1, 0 };

template<typename T>
T gcd(T a, T b) {
	return b ? gcd(b, a % b) : a;
}
template<typename T>
T lcm(T a, T b) {
	return a / gcd(a, b) * b;
}
template<typename T>
int finder(vector<T> vec, T number) {
	auto itr = find(vec.begin(), vec.end(), number);
	size_t index = distance(vec.begin(), itr);
	if (index != vec.size()) return 1;
	else return 0;
}
ll frac(ll n){
	if (n == 0) return 1;
	return (n * frac(n - 1)) % MOD;
}
template<class T> inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template<class T> inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
char mz[2010][2010];
int dp[2010][2010][2];
int main(int argc, char** argv) {
#ifdef HIRO
  string quiz(argv[1]);
  string id(argv[2]);
  string filename("input/" + quiz + "/" + id + ".txt");
  ifstream fin(filename);
  if (fin.peek() == ifstream::traits_type::eof()) {
    cout << "No input.";
    return 0;
  }
  ifstream cin(filename);
  std::cin.rdbuf(cin.rdbuf());
#endif
  ll ans = 0;
  // ll n;
  // cin >> n;
  ll h, w;
  cin >> h >> w;
  // ll n, m, k;
  // cin >> n >> m >> k;
  fi(0, h)
    cin >> mz[i];
  fi(0, h) {
    int start = -1;
    fj(0, w) {
      if(mz[i][j] == '#') {
        if(start != -1) {
          fk(start, j) {
            dp[i][k][0] = j - start;
          }
          start = -1;
        }
      }
      else {
        if(start == -1) {
          start = j;
        }
      }
    }
    if(start != -1) {
      fk(start, w) {
        dp[i][k][0] = w - start;
      }
    }
  }
  // fi(0, h) {
  //   fj(0, w) {
  //     printf("%d ", dp[i][j][0]);
  //   }
  //   printf("\n");
  // }
  fi(0, w) {
    int start = -1;
    fj(0, h) {
      if(mz[j][i] == '#') {
        if(start != -1) {
          fk(start, j) {
            dp[k][i][1] = j - start;
          }
          start = -1;
        }
      }
      else {
        if(start == -1) {
          start = j;
        }
      }
    }
    if(start != -1) {
      fk(start, h) {
        dp[k][i][1] = h - start;
      }
    }
  }
  // fi(0, h) {
  //   fj(0, w) {
  //     printf("%d ", dp[i][j][1]);
  //   }
  //   printf("\n");
  // }
  fi(0, h)
    fj(0, w) {
      if(mz[i][j] == '#')
        continue;
      ll cnt = dp[i][j][0] + dp[i][j][1] - 1;
      chmax(ans, cnt);
    }
  cout << ans << endl;
  return 0;
}



Measured memory_bytes: 35712