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)


// Problem : H - Grid 1
// Contest : AtCoder - Educational DP Contest
// URL : https://atcoder.jp/contests/dp/tasks/dp_h
// Memory Limit : 1024 MB
// Time Limit : 2000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

//Macros

#define ll long long
#define db long double
#define pb push_back
#define eb emplace_back
#define pii pair<int,int>
#define vi vector<int>
#define vii vector<pii>
#define mi map<int,int>
#define mii map<pii,int>
#define fi first
#define se second
#define all(a) (a).begin(),(a).end()
#define sz(x) (int)x.size()
#define mod 1000000007
#define EPS 1e-9
#define io ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#define inf 1e10
#define PI acos(-1.0)
#define int long long
template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define N 1005

//Solution

char a[N][N];
int dp[N][N];

void solve(){
    int n,m;
    cin>>n>>m;
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++) cin>>a[i][j];
    }
    for(int i=0;i<n;i++){
        for(int j=0;j<m;j++){
            if(i == 0 && j == 0) dp[i][j] = 1;
            else{
                if(a[i][j] == '#'){
                    dp[i][j] = 0;
                    continue;
                }
                if(i-1 >= 0) (dp[i][j] += dp[i-1][j]) %= mod;
                if(j-1 >= 0) (dp[i][j] += dp[i][j-1]) %= mod;
            }
        }
    }
    cout<<dp[n-1][m-1]<<endl;
}

signed main(){
    io;
    //freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout);
    int tests;
    //cin>>tests;
    tests = 1;
    while(tests--){
        solve();
    }
    return 0;
}