#include <bits/stdc++.h>
#define ll long long
#define pb push_back
using namespace std;
int n,k;
vector <string> v[51];
ll g[51][1501],used[51][1501];
vector <int> gd[51][1501];
ll p = 1e9+7;
bool check(string s, string l)
{
if(s == l.substr(0,s.size()) or s == l.substr(1))
return true;
else
return false;
}
void answer()
{
string s;
cin >> n >> k;
for(int i = 1; i <= n; i++)
for(int j = 1; j <= k; j++)
{
cin >> s;
v[i].pb(s);
}
for(int i = 0; i < k; i++)
used[1][i] = 1;
for(int m = 1 ; m < n; m++)
for(int i = 0; i < k; i++)
for(int j = 0; j < k; j++)
{
if(used[m][i] == 1)
if(check(v[m][i], v[m+1][j]))
{
gd[m][i].pb(j);
used[m+1][j] = 1;
}
}
for(int i = 0; i < k; i++)
if(used[n][i] == 1)
g[n][i] = 1;
for(int m = n - 1; m > 0; m--)
for(int i = 0; i < k; i++)
if(used[m][i] == 1)
for(int j : gd[m][i] )
if(g[m + 1][j] != 0 )
g[m][i] = (g[m][i] + g[m + 1][j]) % p;
ll pas = 0;
for(int i = 0; i < k; i++)
pas = (pas + g[1][i]) % p;
cout << pas;
}
int main()
{
int t = 1;
//cin >> t;
while(t--)
answer();
return 0;
}
