#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
using vvvll = vector<vector<vector<ll>>>;
using vvvvll = vector<vector<vector<vector<ll>>>>;
using pl4 = pair<ll,ll>;
using str = string;
using vpl4 = vector<pair<ll,ll>>;

#define sz size()
#define be begin()
#define en end()
#define fi first
#define se second
#define pb push_back
#define mp make_pair

#define llin(x) ll (x);cin >>(x);
#define stin(x) str (x);cin >>(x);
#define vllin(x,n) vll (x)(n);FOR(i,0,n-1){cin >>(x)[i];}
#define vllin2(a,b,n) vll (a)(n);vll (b)(n);FOR(i,0,n-1){cin >>(a)[i]>>(b)[i];}
#define vllin3(a,b,c,n) vll (a)(n);vll (b)(n);vll (c)(n);FOR(i,0,n-1){cin >>(a)[i]>>(b)[i]>>(c)[i];}
#define vlling(x,n) (x).assign(n,0);FOR(i,0,n-1){cin >>(x)[i];}
#define vlling2(a,b,n) (a).assign(n,0);(b).assign(n,0);FOR(i,0,n-1){cin >>(a)[i]>>(b)[i];}
#define vlling3(a,b,c,n) (a).assign(n,0);(b).assign(n,0);(c).assign(n,0);FOR(i,0,n-1){cin >>(a)[i]>>(b)[i]>>(c)[i];}
#define vpl4in(x,n) vpl4 (x)((n),mp(0,0));FOR(i,0,n-1){cin >>x[i].fi>>x[i].se;}
#define FOR(i,a,b) for(ll i = a ; i <= b ; i++)
#define rFOR(i,b,a) for(ll i = a; i >= b ; i--)
#define SORT(x) sort(x.be, x.en)
#define rSORT(x) sort(x.rbegin(), x.rend())
#define say(x) cout<<(x);
#define sal(x) cout<<(x)<<endl;
#define says(x) cout<<(x)<<(' ');
#define sas cout<<(' ');
#define sayR(x) cout<<fixed<<setprecision(10)<<(x);
#define salR(x) cout<<fixed<<setprecision(10)<<(x)<<endl;
#define yn(a) cout <<((a)?"yes":"no")<<endl;
#define Yn(a) cout <<((a)?"Yes":"No")<<endl;
#define YN(a) cout <<((a)?"YES":"NO")<<endl;
#define Imp(a) cout <<((a)?"Possible":"Impossible")<<endl;
#define IMP(a) cout <<((a)?"POSSIBLE":"IMPOSSIBLE")<<endl;
#define pow(a,b) ll(pow(a,b))

ll MOD=1000000007;

signed main(){
        llin(h);
        llin(w);
        vector<str> s(h,"");
        FOR(i,0,h-1){
                cin >>s[i];
        }
        vvll ws(h,vll(w,0));
        vvll hs(h,vll(w,0));
        vvll wr(h,vll(w+2,0));
        vvll hr(h+2,vll(w,0));
        ll t=0;
        ll c=0;
        FOR(i,0,h-1){
                t=1;
                c=0;
                FOR(j,0,w-1){
                        if(s[i][j]=='#'){
                                wr[i][t]=c;
                                t++;
                                c=0;
                        }else{
                                ws[i][j]=t;
                                c++;
                        }
                }
                wr[i][t]=c;
        }
        FOR(j,0,w-1){
                t=1;
                c=0;
                FOR(i,0,h-1){
                        if(s[i][j]=='#'){
                                hr[t][j]=c;
                                t++;
                                c=0;
                        }else{
                                hs[i][j]=t;
                                c++;
                        }
                }
                hr[t][j]=c;
        }
        ll k=0;
        FOR(i,0,h-1){
                FOR(j,0,w-1){
                        if(s[i][j]=='.'){
                                k=max(wr[i][ws[i][j]]+hr[hs[i][j]][j],k);
                        }
                }
        }
        sal(k-1)
}


Measured memory_bytes: 129792