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 C++ (GCC 9.2.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;
typedef		 long long int    ll;
typedef		vector<ll>      vll;
#define     fi              first
#define     print(v)        for(ll i:v) cout<<i<<ss
#define     se              second
#define		pb              push_back
#define		nn              "\n"
#define		all(p)          p.begin(),p.end()
#define		zz(v)           (ll)v.size()
#define 	S(a)            scanf("%lld",&a)
#define 	SS(a,b)         scanf("%lld %lld",&a,&b)
#define 	SSS(a,b,c)      scanf("%lld %lld %lld",&a,&b,&c)
#define		ss              ' '
#define     pii             pair<ll,ll>
#define		gcd(a,b)        __gcd(a,b)
#define		lcm(a,b)        (a*b)/gcd(a,b)
const double eps = 1e-8;


int main()
{
    ll mod=1e9+7;

    ll n,m;
    cin>>n>>m;
    string s[n+10];

    for(ll i=0; i<n; i++)
    {
        cin>>s[i];
    }
    ll dp[n][m];
    memset(dp,0,sizeof(dp));

    dp[n-1][m-1]=1;

    for(ll i=n-1; i>=0; i--)
    {
        for(ll j=m-1; j>=0; j--)
        {
            if(s[i][j]!='#')
            {
               // cout<<0;
                ll x=i,y=j-1;

                if(x>=0&&y>=0&&s[x][y]!='#')
                {
                    dp[x][y]+=dp[i][j];
                    dp[x][y]%=mod;

                }
                x=i-1,y=j;
                if(x>=0&&y>=0&&s[x][y]!='#')
                {
                    dp[x][y]+=dp[i][j];
                    dp[x][y]%=mod;

                }
            }
        }
    }


//    for(ll i=0; i<n; i++)
//    {
//        for(ll j=0; j<m; j++)
//        {
//            cout<<dp[i][j]<<ss;
//        }
//        cout<<nn;
//    }

    cout<<dp[0][0]<<nn;



}


/* Final check before submit :

1. array size or integer overflow,like uninitialised 0 index.

2. Think twice,code once.check all possible counter test case.

3. Be careful about corner case! n=1?k=1? something about 0?

4. avoid stupid mistake!complexity(t/m)?precision error?submit same code twice?

5. if got WA than remember that you are missing something common.
   *** Be confident!!! who knows? may be your one step back to AC ***
4. minus mod ans=(ans-k+mod)%mod;

*/