#include <iostream>
#include <map>
#include <set>
using namespace std;
#define int long long
const int N = 1505, mod = 1e9 + 7, C = 256;
int dp[55][N], Ans;
string a[N][N];
map<int, int> mp, mp2;
signed main(){
int n, k;
cin>>n>>k;
for (int i=1;i<=n;i++){
for (int j=1;j<=k;j++)
cin>>a[i][j];
}
for (int i=n;i>=1;i--){
for (int j=1;j<=k;j++){
int h1 = 0, h2 = 0, h3 = 0;
for (int l=1;l<=i;l++){
h1 = (h1 * C + a[i][j][l-1]) % mod;
if (l != i)
h2 = (h2 * C + a[i][j][l-1]) % mod;
if (l != 1)
h3 = (h3 * C + a[i][j][l-1]) % mod;
}
if (i == n)
dp[i][j] = 1;
else
dp[i][j] = mp[h1] % mod;
mp2[h2] += dp[i][j];
mp2[h3] += dp[i][j] * (h2 != h3);
Ans += dp[1][j];
}
mp.clear();
swap(mp2, mp);
}
cout<<Ans % mod<<'\n';
}
