#include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os, const map<T,U>& mp){ os << "{"; for(auto& p : mp){ os << p << ","; } os << "}"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

int main(){
    int h,w; cin >> h >> w;
    vector<string> s(h);
    rep(i,h) cin >> s[i];


    vector<vector<int>> yoko(h,vector<int>(w,0));
    vector<vector<int>> tate(h,vector<int>(w,0));

    rep(i,h){
        rep(j,w){
            if(s[i][j] == '#') continue;
            else if(j==0 or s[i][j-1]=='#'){
                int j2 = j+1;
                while(j2 < w and s[i][j2]=='.'){
                    j2++;
                }
                yoko[i][j] = j2 - j;
            }else{
                yoko[i][j] = yoko[i][j-1];
            }
        }
    }

    rep(j,w){
        rep(i,h){
            if(s[i][j] == '#') continue;
            else if(i==0 or s[i-1][j]=='#'){
                int i2 = i+1;
                while(i2 < h and s[i2][j] == '.'){
                    i2++;
                }
                tate[i][j] = i2-i;
            }else{
                tate[i][j] = tate[i-1][j];
            }
        }
    }

    /* cout << "Yoko" << endl; */
    /* rep(i,h){ */
    /*     rep(j,w){ */
    /*         cout << yoko[i][j] << " "; */
    /*     } */
    /*     cout << endl; */
    /* } */
    /* cout << "tate" << endl; */
    /* rep(i,h){ */
    /*     rep(j,w){ */
    /*         cout << tate[i][j] << " "; */
    /*     } */
    /*     cout << endl; */
    /* } */


    /* cout << "plus" << endl; */
    /* rep(i,h){ */
    /*     rep(j,w){ */
    /*         cout << tate[i][j] + yoko[i][j] << " "; */
    /*     } */
    /*     cout << endl; */
    /* } */

    int ans = 0;
    rep(i,h)rep(j,w){
        ans = max(ans,tate[i][j]+yoko[i][j]-1);
    }
    cout << ans << endl;
}


Measured memory_bytes: 35712