Problem:
Score : 400 points

Problem Statement

There is a grid with H horizontal rows and W vertical columns, and there are obstacles on some of the squares.

Snuke is going to choose one of the squares not occupied by an obstacle and place a lamp on it.
The lamp placed on the square will emit straight beams of light in four cardinal directions: up, down, left, and right.
In each direction, the beam will continue traveling until it hits a square occupied by an obstacle or it hits the border of the grid. It will light all the squares on the way, including the square on which the lamp is placed, but not the square occupied by an obstacle.

Snuke wants to maximize the number of squares lighted by the lamp.

You are given H strings S_i (1 \leq i \leq H), each of length W. If the j-th character (1 \leq j \leq W) of S_i is #, there is an obstacle on the square at the i-th row from the top and the j-th column from the left; if that character is ., there is no obstacle on that square.

Find the maximum possible number of squares lighted by the lamp.

Constraints

1 \leq H \leq 2,000

1 \leq W \leq 2,000

S_i is a string of length W consisting of # and ..

. occurs at least once in one of the strings S_i (1 \leq i \leq H).

Input

Input is given from Standard Input in the following format:

H W
S_1
:
S_H

Output

Print the maximum possible number of squares lighted by the lamp.

Sample Input 1

4 6
#..#..
.....#
....#.
#.#...

Sample Output 1

8

If Snuke places the lamp on the square at the second row from the top and the second column from the left, it will light the following squares: the first through fifth squares from the left in the second row, and the first through fourth squares from the top in the second column, for a total of eight squares.

Sample Input 2

8 8
..#...#.
....#...
##......
..###..#
...#..#.
##....#.
#...#...
###.#..#

Sample Output 2

13

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.IOException;
import java.io.InputStream;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;

public class Main {

	static Scanner sc = new Scanner(System.in);

	static class FastScanner {
		private final InputStream in;
		private final byte[] buffer = new byte[1024];
		private int ptr = 0;
		private int buflen = 0;

		public FastScanner(InputStream source) {
			in = source;
		}

		private boolean hasNextByte() {
			if (ptr < buflen) {
				return true;
			} else {
				ptr = 0;
				try {
					buflen = in.read(buffer);
				} catch (IOException e) {
					e.printStackTrace();
				}
				if (buflen <= 0) {
					return false;
				}
			}
			return true;
		}

		private int readByte() {
			if (hasNextByte())
				return buffer[ptr++];
			else
				return -1;
		}

		private static boolean isPrintableChar(int c) {
			return 33 <= c && c <= 126;
		}

		public boolean hasNext() {
			while (hasNextByte() && !isPrintableChar(buffer[ptr]))
				ptr++;
			return hasNextByte();
		}

		public String next() {
			if (!hasNext())
				throw new NoSuchElementException();
			StringBuilder sb = new StringBuilder();
			int b = readByte();
			while (isPrintableChar(b)) {
				sb.appendCodePoint(b);
				b = readByte();
			}
			return sb.toString();
		}

		public long nextLong() {
			if (!hasNext())
				throw new NoSuchElementException();
			long n = 0;
			boolean minus = false;
			int b = readByte();
			if (b == '-') {
				minus = true;
				b = readByte();
			}
			if (b < '0' || '9' < b) {
				throw new NumberFormatException();
			}
			while (true) {
				if ('0' <= b && b <= '9') {
					n *= 10;
					n += b - '0';
				} else if (b == -1 || !isPrintableChar(b)) {
					return minus ? -n : n;
				} else {
					throw new NumberFormatException();
				}
				b = readByte();
			}
		}

		public int nextInt() {
			long nl = nextLong();
			if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
				throw new NumberFormatException();
			return (int) nl;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}
	}

	/**
	 * Compute n! mod. p, (n!)^(-1) mod.p
	 *
	 * @param fac[]
	 *            : n! mod. p
	 * @param finv[]
	 *            : (n!)^(-1) mod. p
	 * @param MAX
	 *            :
	 * @param MOD
	 *            :
	 */

	static void hz_COMinit(long fac[], long finv[], long inv[], final int MAX, final long MOD) {
		fac[0] = fac[1] = 1L;
		finv[0] = finv[1] = 1L;
		inv[1] = 1L;
		for (int i = 2; i < MAX; i++) {
			fac[i] = fac[i - 1] * i % MOD;
			inv[i] = MOD - inv[(int) (MOD % i)] * (MOD / i) % MOD;
			finv[i] = finv[i - 1] * inv[i] % MOD;
		}
	}
	/*
	 * static void hz_COMinit(long fac[], long finv[], long inv[],final int MAX,
	 * final long MOD) { fac[0] = fac[1] = 1L; finv[0] = finv[1] = 1L; inv[1] =
	 * 1L; for (int i = 2; i < MAX; i++){ fac[i] = (BigInteger.valueOf(fac[i -
	 * 1]).multiply(BigInteger.valueOf(i)).mod(BigInteger.valueOf(MOD))).
	 * longValue(); inv[i] =
	 * (BigInteger.valueOf(MOD).subtract(BigInteger.valueOf(inv[(int)(MOD%i)]).
	 * multiply(BigInteger.valueOf(MOD/i)).mod(BigInteger.valueOf(MOD)))).
	 * longValue(); finv[i] = (BigInteger.valueOf(finv[i -
	 * 1]).multiply(BigInteger.valueOf(inv[i])).mod(BigInteger.valueOf(MOD))).
	 * longValue(); } }
	 */

	/**
	 * @Compute nCk(二項係数計算) mod. p
	 * @param fac[]
	 *            : n! mod. p
	 * @param finv[]
	 *            : (n!)^(-1) mod. p
	 * @return :nCk(二項係数計算) mod. p
	 */
	static long hz_COM(long fac[], long finv[], int n, int k, final long MOD) {
		if (n < k)
			return 0;
		if (n < 0 || k < 0)
			return 0;
		return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
	}
	/*
	 * static long hz_COM(long fac[],long finv[], int n, int k, final long MOD){
	 * if (n < k) return 0; if (n < 0 || k < 0) return 0; return
	 * BigInteger.valueOf(fac[n]) .multiply(BigInteger.valueOf(finv[k])
	 * .multiply(BigInteger.valueOf(finv[n - k])) .mod(BigInteger.valueOf(MOD))
	 * ) .mod(BigInteger.valueOf(MOD)).longValue(); }
	 */

	static int hz_swap(int a, int b) {
		if (a >= b)
			return a;
		else
			return b;
	}

	static long hz_swap(long a, long b) {
		if (a >= b)
			return a;
		else
			return b;
	}

	// mod上での差分
	static long hz_modSub(long a, long b, long mod) {
		long v = a - b;
		if (v < 0)
			v += mod;
		return v % mod;
	}

	// mod上での割算
	static long hz_modDiv(long a, long b, long mod) {
		return (a % mod) * hz_modInv(b, mod) % mod;
	}

	// 逆元
	static long hz_modInv(long a, long mod) {
		return hz_modPow(a, mod - 2L, mod);
	}

	// mod上での累乗
	static long hz_modPow(long n, long k, long mod) {

		long result = 1L;

		// k を右シフトしつつ n を 2 乗していく
		while (k > 0L) {
			// k の最下ビットが 1 なら、今の n を答えに掛ける
			if ((k & 1L) == 1L)
				result = (result * n) % mod;
			n = n * n % mod;
			k >>= 1L;
		}

		return result;
	}

	// Union Find Tree
	static class HZ_UF {

		public int[] par;
		public int[] rank;

		public HZ_UF(int n) {
			this.par = new int[n + 1];
			this.rank = new int[n + 1];

			Arrays.fill(par, -1);
			Arrays.fill(rank, 0);
		}

		public void unite(int x, int y) {
			link(root(x), root(y));
		}

		public boolean link(int x, int y) {
			if (x == y)
				return false;
			if (rank[x] > rank[y]) {
				par[x] += par[y];
				par[y] = x;
			} else {
				par[y] += par[x];
				par[x] = y;
				if (rank[x] == rank[y])
					rank[y]++;
			}
			return true;
		}

		public boolean isSame(int x, int y) {
			return root(x) == root(y);
		}

		public int root(int x) {
			if (par[x] < 0)
				return x;
			else
				return x = root(par[x]);
		}

		public int size(int x) {
			return -par[root(x)];
		}
	}

	public static void main(String[] args) {

		solve_abc129_d();
	}
  
  	public static void solve_abc129_d() {

		FastScanner sc = new FastScanner(System.in);
		
		int h = sc.nextInt();
		int w = sc.nextInt();
		
		String[] s = new String[h+1];
		for(int i=1;i<=h;i++) s[i] = sc.next();
		
		int[][] hc = new int[h+1][w+1];
		int[][] wc = new int[h+1][w+1];
		int[][] hwc = new int[h+1][w+1];
		
		for(int i=1;i<=h;i++){
			int j =1;
			int tmpCount = 0;
			int startj = 1;
			while(j <= w){
				char c = s[i].charAt(j-1);
				if(c == '.'){
					tmpCount++;
					if(j == w){
						for(int k = startj; k<=j;k++){
							wc[i][k] = tmpCount;
						}
					}
				}
				else{
					for(int k = startj; k<j;k++){
							wc[i][k] = tmpCount;
					}
					tmpCount = 0;
					startj = j + 1;
				}
				j++;
			}
		}
		
		for(int i=1;i<=w;i++){
			int j=1;
			int tmpCount = 0;
			int startj = 1;
			while(j <= h){
				char c = s[j].charAt(i-1);
				if(c == '.'){
					tmpCount++;
					if(j == h){
						for(int k = startj; k<=j;k++){
							hc[k][i] = tmpCount;
						}
					}				
				}
				else{
					for(int k = startj; k<j;k++){
							hc[k][i] = tmpCount;
					}
					tmpCount = 0;
					startj = j + 1;
				}
				j++;
			}
		}
		
		int max = 0;
		for(int i=1;i<=h;i++){
			for(int j=1;j<=w;j++){
				if(s[i].charAt(j-1) == '.'){
					hwc[i][j] = hc[i][j] + wc[i][j] - 1;
					max = Math.max(max, hwc[i][j]);
				}
			}
		}
		
		/*
		for(int i=1;i<=h;i++){
			for(int j=1;j<=w;j++){
				System.out.print("\t" + wc[i][j]);
			}
			System.out.println();
		}
		System.out.println();

		for(int i=1;i<=h;i++){
			for(int j=1;j<=w;j++){
				System.out.print("\t" + hc[i][j]);
			}
			System.out.println();
		}
		*/
		
		System.out.println(max);

	}
}