Problem:
Score : 100 points

Problem Statement

There is a grid with H horizontal rows and W vertical columns.
Let (i, j) denote the square at the i-th row from the top and the j-th column from the left.

For each i and j (1 \leq i \leq H, 1 \leq j \leq W), Square (i, j) is described by a character a_{i, j}.
If a_{i, j} is ., Square (i, j) is an empty square; if a_{i, j} is #, Square (i, j) is a wall square.
It is guaranteed that Squares (1, 1) and (H, W) are empty squares.

Taro will start from Square (1, 1) and reach (H, W) by repeatedly moving right or down to an adjacent empty square.

Find the number of Taro's paths from Square (1, 1) to (H, W).
As the answer can be extremely large, find the count modulo 10^9 + 7.

Constraints

H and W are integers.

2 \leq H, W \leq 1000

a_{i, j} is . or #.

Squares (1, 1) and (H, W) are empty squares.

Input

Input is given from Standard Input in the following format:

H W
a_{1, 1}\ldotsa_{1, W}
:
a_{H, 1}\ldotsa_{H, W}

Output

Print the number of Taro's paths from Square (1, 1) to (H, W), modulo 10^9 + 7.

Sample Input 1

3 4
...#
.#..
....

Sample Output 1

3

There are three paths as follows:

Sample Input 2

5 2
..
#.
..
.#
..

Sample Output 2

0

There may be no paths.

Sample Input 3

5 5
..#..
.....
#...#
.....
..#..

Sample Output 3

24

Sample Input 4

20 20
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................
....................

Sample Output 4

345263555

Be sure to print the count modulo 10^9 + 7.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

/******************************************
 *  Author : Atul Anand   
 *  Created On : Sat Feb 08 2020
 *******************************************/

import java.io.*;
import java.util.*;

public class Main{
    
    public static void main(String[] args) throws IOException {
        int H=in.nextInt();
        int W=in.nextInt();
        int a[][]=new int[H][W];
        for(int i=0;i<H;i++){
            String S=in.next();
            for(int j=0;j<W;j++){
                a[i][j]= S.charAt(j)=='.' ? 0 : 1;
            }
        }
        long dp[][]=new long[H][W];
        int mod=(int)1e9+7;
        for(int i=0;i<W;i++){
            if(a[0][i]==1){
                break;
            }
            dp[0][i]=1;
        }
        for(int i=0;i<H;i++){
            if(a[i][0]==1){
                break;
            }
            dp[i][0]=1;
        }

        for(int i=1;i<H;i++){
            for(int j=1;j<W;j++){
                if(a[i][j]!=1){
                    dp[i][j]=(dp[i-1][j]+dp[i][j-1])%mod;
                }
            }
        }
        println(dp[H-1][W-1]);
        in.close();
        out.close();
    }

    static int MIN = Integer.MIN_VALUE;
    static int MAX = Integer.MAX_VALUE;
    static Reader in = new Reader();
    static PrintWriter out = new PrintWriter(System.out);
    static void read(int arr[], int N) throws IOException{ for(int i=0;i<N;i++){ arr[i]=in.nextInt(); } }
    static void read(long arr[], int N) throws IOException{ for(int i=0;i<N;i++){ arr[i]=in.nextLong(); } }
    static void read(String arr[], int N) throws IOException{ for(int i=0;i<N;i++){ arr[i]=in.next(); } }
    static void print(Object O){ out.print(O); }
    static void println(Object O){ out.println(O); }
    static void print(int arr[]){ for(int i=0;i<arr.length;i++){ print(arr[i]+" "); } println(""); }
    static void print(int arr[][]){ for(int i=0;i<arr.length;i++){ print(arr[i]); } }
    static void debug(Object O){ System.out.println(O); }
}

class Reader {
    BufferedReader reader;
    StringTokenizer tokenizer;

    Reader() {
        reader = new BufferedReader(new InputStreamReader(System.in));
        tokenizer = new StringTokenizer("");
    }

    String next() throws IOException {
        while (!tokenizer.hasMoreTokens() ) { tokenizer=new StringTokenizer(reader.readLine()); }
        return tokenizer.nextToken();
    }

    int nextInt() throws IOException { return Integer.parseInt(next()); }
    double nextDouble() throws IOException { return Double.parseDouble(next()); }
    long nextLong() throws IOException { return Long.parseLong(next()); }
    String nextLine() throws IOException { return reader.readLine(); }
    void close() throws IOException { reader.close(); }
}