#include <vector>
#include <list>
#include <map>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <cstdio>
#include <climits>
#include <complex>
#include <cstdint>
#include <tuple>

#define M_PI       3.14159265358979323846

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
inline int readInt() { int x; scanf("%d", &x); return x; }

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;

//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define SQ(a) ((a)*(a))
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,s,n) for(int i=s;i<(int)n;++i)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
struct Edge {
    int to, cost;
    Edge(int to, int cost): to(to), cost(cost) {}
};

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<Edge>> AdjList;
AdjList graph;

const int INF = 100000000;

int N, M;
int h[2010][2010]; /* 縦 横 */
int w[2010][2010]; /* 横 縦 */
vector<string> field;
int main() {
    //cout << fixed << setprecision(15);
   int H, W; cin >> H >> W;
    REP(i, H){
        string s; cin >> s;
        field.push_back(s);
    }


    for(int i=0; i<H; ++i){
        for(int j=0; j<W; ++j){
            if(field[i][j]=='.'){
                if(j==0){
                    w[i][j] = 1;
                }else{
                    w[i][j] = w[i][j-1]+1;
                }
            }else if(field[i][j]=='#'){
                w[i][j] = 0;
            }
        }
    }

    for(int i=0; i<W; ++i){
        for(int j=0; j<H; ++j){
            if(field[j][i]=='.'){
                if(j==0){
                    h[j][i] = 1;
                }else{
                    h[j][i] = h[j-1][i]+1;
                }
            }else if(field[j][i]=='#'){
                h[j][i] = 0;
            }
        }
    }

    for(int i=0; i<H; ++i){
        int maxV = 0;
        for(int j=W-1; j>=0; --j){
            if(w[i][j] == 0) {
                maxV = 0;
            }else {
                maxV = max(maxV, w[i][j]);
                w[i][j] = maxV;
            }
        }
    }
    for(int i=0; i<W; ++i){
        int maxV = 0;
        for(int j=H-1; j>=0; --j){
            if(h[j][i] == 0) {
                maxV = 0;
            }else {
                maxV = max(maxV, h[j][i]);
                h[j][i] = maxV;
            }
        }
    }

    int ans = 0;
    for(int i=0; i<H; ++i){
        for(int j=0; j<W; ++j){
            ans = max(ans, h[i][j] + w[i][j]-1);
        }
    }
    cout << ans << endl;
    return 0;
}

Measured memory_bytes: 35840