#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(), x.end()
const long long P = 31;
const long long HashMod = 1e9 + 123;
const int MOD = 1e9 + 7;
int main() {
#ifdef judge
ifstream cin("input.txt");
#endif // judge
ios_base :: sync_with_stdio(0);
cin.tie(0) , cout.tie(0);
int n , k;
cin >> n >> k;
vector<long long> pow;
pow.push_back(1LL);
while ((int)pow.size() <= n) {
pow.push_back(1LL * pow.back() * P % MOD);
}
auto getHash = [&](string s) {
int res = 0;
for (int i = 0; i < (int)s.size(); i++) {
res += ((1LL * s[i] * pow[i]) % MOD);
res %= MOD;
}
return res;
};
int full[n][k] , pref[n][k] , suf[n][k];
for (int i = 0; i < n; i++) {
for (int j = 0; j < k; j++) {
string x;
cin >> x;
full[i][j] = getHash(x);
if (i > 0) {
pref[i][j] = getHash(x.substr(0 , i));
suf[i][j] = getHash(x.substr(1 , i));
}
}
}
vector<vector<int> > dp(n , vector<int>(k , 0));
for (int j = 0; j < k; j++) {
dp[0][j] = 1;
}
for (int i = 1; i < n; i++) {
for (int cur = 0; cur < k; cur++) {
for (int prev = 0; prev < k; prev++) {
if (full[i - 1][prev] == pref[i][cur] || full[i - 1][prev] == suf[i][cur]) {
dp[i][cur] += dp[i - 1][prev];
dp[i][cur] %= MOD;
}
}
}
}
int ans = 0;
for (int j = 0; j < k; j++) {
ans += dp[n - 1][j];
ans %= MOD;
}
cout << ans << '\n';
return 0;
}
