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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

/* attention
    long longのシフト演算には気をつけよう
    タイポした時のデバッグが死ぬほどきつくなるので変数名は最低3字くらい使った方がいいかも
    sizeは(int)とキャストしよう
    ごちゃごちゃ場合分けを考える前に全探索は考えましたか？
*/

const ll mod = 1e9+7;

void chmod(ll &M){
    if(M >= mod) M %= mod;
    else if(M < 0){
        M += (abs(M)/mod + 1)*mod;
        M %= mod;
    }
}

ll modpow(ll x, ll n){
    if(n == 0) return 1;

    ll res = modpow(x, n/2);
    if(n%2 == 0) return res*res%mod;
    else return res*res%mod*x%mod;
}

ll power(ll x, ll n){
    if(n == 0) return 1;

    ll res = power(x, n/2);
    if(n%2 == 0) return res*res;
    else return res*res*x;
}

int getl(int i, int N) { return i==0? N-1:i-1; };
int getr(int i, int N) { return i==N-1? 0:i+1; };

/* <--------------------------------------------> */

int H, W;

vector< vector<char> > fi(1010, vector<char>(1010, '#'));
vector< vector<ll> > dp(1010, vector<ll>(1010, 0));

const int d1[4] = {0,1,0,-1};
const int d2[4] = {1,0,-1,0};



int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> H >> W;
    for(int i=1; i<=H; ++i) for(int j=1; j<=W; ++j) cin >> fi[i][j];

    dp[1][1] = 1;
    for(int i=1; i<=H; ++i){
        for(int j=1; j<=W; ++j){
            if(fi[i][j] == '#') continue;
            dp[i][j] += dp[i-1][j] + dp[i][j-1];
            chmod(dp[i][j]);
        }
    }

    cout << dp[H][W] << endl;

    // for(int i=1; i<=H; ++i){
    //     for(int j=1; j<=W; ++j){
    //         printf("%5lld", dp[i][j]);
    //     }
    //     cout << endl;
    // }

	return 0;
}