/**
* author: kututay
* created: 06.09.2023 16:41:38
**/
#include <bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include "/Users/kutay/CP/templates/debug.h"
#else
#define debug(...) void(38)
#endif
#define int long long
const int mod = 1e9 + 7;
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int n, k; cin >> n >> k;
vector<vector<int>> a(n * k + 2);
vector<int> dp(n * k + 2, -1), cnt(n * k + 2);
function<int(int)> f = [&](int node) {
if (dp[node] != -1) return dp[node];
int res = 0;
sort(a[node].begin(), a[node].end());
for (int i = 0; i < (int) a[node].size(); i++) {
int next = a[node][i];
if (i > 0 && a[node][i - 1] == next) continue;
res += (cnt[node] * f(next)) % mod;
res %= mod;
}
return dp[node] = res;
};
map<string, int> m;
int count = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < k; j++) {
string s; cin >> s;
if (m.count(s) == 0) {
m[s] = ++count;
}
int node = m[s];
cnt[node]++;
if (i == n - 1) dp[node] = cnt[node];
if (i > 0) {
if (m.count(s.substr(0, i))) a[m[s.substr(0, i)]].emplace_back(node);
if (m.count(s.substr(1, i))) a[m[s.substr(1, i)]].emplace_back(node);
} else {
if (cnt[node] == 1) {
a[n * k + 1].emplace_back(node);
}
}
}
}
cnt[n * k + 1] = 1;
cout << f(n * k + 1) << '\n';
}
