#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll N = 55, K = 1505;
const ll base = 727, mod = 1e9 + 7;
ll n, k, hsh[N][K], inv = 696011009, pwr[N];
vector<pair<ll, ll>> g[N][K];
map<ll, ll> cnt[N], dp[N];
int main(){
pwr[0] = 1;
for (ll i = 1; i < N; i ++)
pwr[i] = (pwr[i - 1] * base) % mod;
cin >> n >> k;
for (ll i = 1; i <= n; i ++){
for (ll j = 1; j <= k; j ++){
string s;
cin >> s;
for (char c : s)
hsh[i][j] = (hsh[i][j] * base + c) % mod;
cnt[i][hsh[i][j]]++;
dp[i][hsh[i][j]]++;
}
}
// cout << endl;
// for (int i = 1; i <= n; i ++){
// cout << i << " : ";
// for (auto [H, val] : dp[i])
// cout << H << " -- " << val << ", ";
// cout << endl;
// }
// cout << endl;
for (ll i = n - 1; i > 0; i --){
for (auto [H, C] : cnt[i]){
ll sm = 0;
// cout << "HASH = " << H << endl;
map<int, bool> seen;
for (int c = 'a'; c <= 'z'; c ++){
ll nh = (H * base + c) % mod;
// cout << "can have edge with " << nh << endl;
if (!seen[nh] and dp[i + 1].find(nh) != dp[i + 1].end())
sm = (sm + dp[i + 1][nh]) % mod;
seen[nh] = 1;
nh = (H + pwr[i] * c) % mod;
// cout << "can have edge with " << nh << endl;
if (!seen[nh] and dp[i + 1].find(nh) != dp[i + 1].end())
sm = (sm + dp[i + 1][nh]) % mod;
seen[nh] = 1;
}
dp[i][H] = C * sm % mod;
}
}
// cout << endl;
// for (int i = 1; i <= n; i ++){
// cout << i << " : ";
// for (auto [H, val] : dp[i])
// cout << H << " -- " << val << ", ";
// cout << endl;
// }
// cout << endl;
ll ans = 0;
for (auto [H, val] : dp[1])
ans = (ans + val) % mod;
cout << ans << endl;
}
