# include <bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
template<typename T>vector<T> make_v(size_t a){ return vector<T>(a); }
template<typename T,typename... Ts>auto make_v(size_t a, Ts... ts){ return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...)); }
template<typename T,typename V>typename enable_if<is_class<T>::value==0>::type fill_v(T &t, const V &v){ t = v; }
template<typename T,typename V>typename enable_if<is_class<T>::value!=0>::type fill_v(T &t, const V &v){ for(auto &e : t) fill_v(e, v); }
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        sort(ALL((wpwpw)));(wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)

int h, w;
char c[2020][2020];
int cnt[4][2020][2020];
int main(){
    cin >> h >> w;
    for(int i = 1;i <= h;i++)for(int j = 1;j <= w;j++){
        cin >> c[i][j];
    }
    for(int i = 1;i <= h;i++){
        for(int j = 1;j <= w;j++){
            if(i == 1){
                if(c[i][j] == '.')cnt[0][i][j] = 1;
            }else{
                if(c[i][j] == '.')cnt[0][i][j] = cnt[0][i - 1][j] + 1;
            }
        }
    }
    for(int i = h;i >= 1;i--){
        for(int j = 1;j <= w;j++){
            if(i == h){
                if(c[i][j] == '.')cnt[1][i][j] = 1;
            }else{
                if(c[i][j] == '.')cnt[1][i][j] = cnt[1][i + 1][j] + 1;
            }
        }
    }
    for(int i = 1;i <= h;i++){
        for(int j = 1;j <= w;j++){
            if(j == 1){
                if(c[i][j] == '.')cnt[2][i][j] = 1;
            }else{
                if(c[i][j] == '.')cnt[2][i][j] = cnt[2][i][j - 1] + 1;
            }
        }
    }
    for(int i = 1;i <= h;i++){
        for(int j = w;j >= 1;j--){
            if(j == w){
                if(c[i][j] == '.')cnt[3][i][j] = 1;
            }else{
                if(c[i][j] == '.')cnt[3][i][j] = cnt[3][i][j + 1] + 1;
            }
        }
    }
    int ans = 0;
    for(int i = 1;i <= h;i++){
        for(int j = 1;j <= w;j++){
            int num = 0;
            REP(k, 4)num += cnt[k][i][j];
            ans = max(ans, num - 3);
        }
    }
    cout << ans << endl;
}

Measured memory_bytes: 67968