#include <bits/stdc++.h>
#define endl "\n"
#define pb push_back
#define int long long
using namespace std;
const int inf = 2e18 + 5;
const int N = 5e3 + 5;
const int mod = 1e9 + 7;
int32_t main(){
//freopen("in.txt","r", stdin);
int n, k;
cin>>n>>k;
vector<vector<string> > a(n, vector<string>(k));
map<string, vector<int> > mp;
for(int i = 0; i < n; i++){
for(int j = 0; j < k; j++){
cin>>a[i][j];
mp[a[i][j]].pb(j);
}
}
vector<vector<int> > dp(n+1, vector<int>(k));
for(int i = 0; i < k; i++){
dp[0][i] = 1;
}
for(int i = 0; i < n-1; i++){
for(int j = 0; j < k; j++){
string s1 = a[i+1][j].substr(0, a[i+1][j].size()-1);
string s2 = a[i+1][j].substr(1, a[i+1][j].size()-1);
for(auto itr: mp[s1]){
dp[i+1][j] = (dp[i+1][j] + dp[i][itr])%mod;
//cout<<s1<<" "<<itr<<endl;
}
if(s1 == s2) continue;
for(auto itr: mp[s2]){
dp[i+1][j] = (dp[i+1][j] + dp[i][itr])%mod;
//cout<<s2<<" "<<itr<<endl;
}
}
}
int s = 0;
for(int i = 0; i < k; i++){
s = (s + dp[n-1][i])%mod;
}
cout<<s<<endl;
return 0;
}
