#include <bits/stdc++.h>
using namespace std;
#define SZ(x) (int)(x).size()
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define RFOR(i,a,b) for (int i=(a);i>=(b);--i)
const int MX_N = 55;
const int MX_K = 1505;
const int MOD = 1e9+7;
int N, K;
string S[MX_N][MX_K];
int dp[MX_N][MX_K];
vector<int> build_table(string W) {
vector<int> T(W.length()+1);
int pos = 1; // the current position we are computing in T
int cnd = 0; // the zero-based index in W of the next character of the current candidate substring
T[0] = -1;
while (pos < (int)W.length()) {
if (W[pos] == W[cnd])
T[pos] = T[cnd];
else {
T[pos] = cnd;
cnd = T[cnd]; // (to increase performance)
while (cnd >= 0 and W[pos] != W[cnd]) {
cnd = T[cnd];
}
}
pos = pos + 1, cnd = cnd + 1;
}
T[pos] = cnd; // (only need when all word occurrences searched)
return T;
}
bool search(string S, string W, vector<int>& T) {
int P[S.length()];
int nP;
int j = 0;
int k = 0;
nP = 0;
while (j < (int)S.length()) {
if (W[k] == S[j]) {
j = j + 1;
k = k + 1;
if (k == (int)W.length()) {
// (occurrence found, if only first occurrence is needed, m <- j - k may be returned here)
P[nP] = j - k, nP = nP + 1;
k = T[k]; // (T[length(W)] can't be -1)
}
}
else {
k = T[k];
if (k < 0) {
j = j + 1;
k = k + 1;
}
}
}
return nP > 0;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cin >> N >> K;
FOR(i,1,N){
FOR(j,1,K) cin >> S[i][j];
}
FOR(j,1,K) dp[N][j] = 1;
RFOR(i,N-1,1){
FOR(j,1,K){
dp[i][j] = 0;
vector<int> T = build_table(S[i][j]);
FOR(k,1,K) {
if (search(S[i+1][k], S[i][j], T)) {
//cout << i << " " << j << " :: " << i+1 << " " << k << endl;
dp[i][j] += dp[i+1][k];
if (dp[i][j] >= MOD) dp[i][j] -= MOD;
}
}
}
}
int ans = 0;
FOR(i,1,K){
ans += dp[1][i];
if (ans >= MOD) ans -= MOD;
}
cout << ans << '\n';
}
