/**
* 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<string>> a(n, vector<string>(k));
for (int i = 0; i < n; i++) {
for (int j = 0; j < k; j++) {
cin >> a[i][j];
}
}
vector<vector<int>> dp(n, vector<int>(k, -1));
for (int i = 0; i < k; i++) {
dp[0][i] = 1;
}
for (int i = 1; i < n; i++) {
for (int j = 0; j < k; j++) {
int b = 0;
for (int l = 0; l < k; l++) {
if (a[i - 1][l] == a[i][j].substr(0, i) || a[i - 1][l] == a[i][j].substr(1, i)) {
b += dp[i - 1][l];
b %= mod;
}
}
dp[i][j] = b % mod;
}
}
int ans = 0;
for (int i = 0; i < k; i++) {
ans += dp[n - 1][i];
ans %= mod;
}
cout << ans << '\n';
}
