#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 2e5 + 5, MOD = 1e9 + 7, p = 29;
ll dp[55][1505], h[55][1505][3], us[60];
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
us[0] = 1;
for(int i = 1; i < 60; i++)
{
us[i] = (us[i - 1] * p) % MOD;
}
int n, k;
cin >> n >> k;
for(int i = 1; i <= n; i++)
{
for(int j = 1; j <= k; j++)
{
string str;
cin >> str;
str = "#" + str;
for(int l = 1; l <= i; l++)
{
h[i][j][0] = (h[i][j][0] + (str[l] - 'a' + 1) * us[l]) % MOD;
if(l == i - 1)
h[i][j][1] = h[i][j][0];
}
for(int l = 2; l <= i; l++)
{
h[i][j][2] = (h[i][j][2] + (str[l] - 'a' + 1) * us[l - 1]) % MOD;
}
// cout << i << " " << j << " " << h[i][j][0] << " " << h[i][j][1] << " " << h[i][j][2] << '\n';
}
}
for(int i = 1; i <= k; i++)
dp[1][i] = 1;
for(int i = 1; i < n; i++)
{
for(int j = 1; j <= k; j++)
{
for(int l = 1; l <= k; l++)
{
if(h[i][j][0] == h[i + 1][l][1])
{
if(dp[i + 1][l] == 0)
{
dp[i + 1][l] = dp[i][j];
}
else
{
dp[i + 1][l] = (dp[i + 1][l] + dp[i][j]) % MOD;
}
}
else if(h[i][j][0] == h[i + 1][l][2])
{
if(dp[i + 1][l] == 0)
{
dp[i + 1][l] = dp[i][j];
}
else
{
dp[i + 1][l] = (dp[i + 1][l] + dp[i][j]) % MOD;
}
}
}
}
}
// for(int i = 1; i <= n; i++)
// {
// for(int j = 1; j <= k; j++)
// {
// cout << dp[i][j] << " " ;
// }
// cout << '\n';
// }
ll ans = 0;
for(int i = 1; i <= k; i++)
ans = (ans + dp[n][i]) % MOD;
cout << ans << '\n';
}
