#include <bits/stdc++.h>
#pragma GCC optimize ("O2")
#pragma GCC optimize ("unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) {cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;}
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;
const ld eps=1e-7;
const int inf=1000000010;
const ll INF=10000000000000010LL;
const int mod = 1000000007;
const int N = 53, K = 1510, SGM=26;
int n, m, k, u, v, x, y, t, a, b;
int TR[N*K][26], ts;
ll sum[N*K];
ll dp[N][K];
string S[N][K];
int AddTrie(string &s){
int v=0;
for (char ch:s){
if (!TR[v][ch-'a']) TR[v][ch-'a']=++ts;
v=TR[v][ch-'a'];
}
return v;
}
ll Get(string &s){
int v=0;
for (char ch:s){
if (!TR[v][ch-'a']) return 0;
v=TR[v][ch-'a'];
}
return sum[v];
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
cin>>n>>k;
for (int i=1; i<=n; i++) for (int j=1; j<=k; j++) cin>>S[i][j];
for (int j=1; j<=k; j++) dp[1][j]=1;
for (int i=2; i<=n; i++){
memset(TR, 0, sizeof(TR));
memset(sum, 0, sizeof(sum));
ts=0;
for (int j=1; j<=k; j++){
int v=AddTrie(S[i-1][j]);
sum[v]+=dp[i-1][j];
}
for (int j=1; j<=k; j++){
string s=S[i][j].substr(0, i-1), t=S[i][j].substr(1, i-1);
dp[i][j]=Get(s);
if (s!=t) dp[i][j]+=Get(t);
dp[i][j]%=mod;
}
}
ll ans=0;
for (int j=1; j<=k; j++) ans=(ans+dp[n][j])%mod;
cout<<ans<<'\n';
return 0;
}
