// author: MisterReaper (Ahmet Alp Orakci)
#include <bits/stdc++.h>
using namespace std;
#define int long long
const int MOD = 1e9 + 7;
#define ONLINE_JUDGE
#ifndef ONLINE_JUDGE
#include "debug.h"
#define OPEN freopen(".in", "r", stdin); freopen(".out", "w", stdout);
#define TIME cerr << "\n" << fixed << setprecision(2) << 1000.0 * clock() / CLOCKS_PER_SEC << " milliseconds ";
#else
#define debug(...) void(23)
#define OPEN void(0000)
#define TIME void(232323233)
#endif
void solve()
{
int n, k; cin >> n >> k;
vector <vector <string>> arr(n +1, vector <string> (k +1));
for(int i = 1; i <= n; i++)
{
for(int j = 1; j <= k; j++) cin >> arr[i][j];
}
map <string, int> mp;
sort(arr[1].begin(), arr[1].end());
arr[1].erase(unique(arr[1].begin(), arr[1].end()), arr[1].end());
k = arr[1].size();
for(int i = 1; i < k; i++) mp[arr[1][i]]++;
for(int i = 2; i <= n; i++)
{
sort(arr[i].begin(), arr[i].end());
arr[i].erase(unique(arr[i].begin(), arr[i].end()), arr[i].end());
k = arr[i].size();
for(int j = 1; j < k; j++)
{
string f, s = arr[i][j];
for(int l = 2; l <= i; l++) f += arr[i][j][l -1];
s.pop_back();
mp[arr[i][j]] += mp[f] + (f != s ? mp[s] : 0);
mp[arr[i][j]] %= MOD;
debug(arr[i][j], mp[arr[i][j]]);
}
}
int ans = 0;
k = arr[n].size();
for(int i = 1; i < k; i++)
{
ans += mp[arr[n][i]];
ans %= MOD;
}
cout << ans << "\n";
return;
}
int32_t main()
{
OPEN;
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
int t = 1; //cin >> t;
while(t--)
{
solve();
}
TIME;
return 0;
}
