#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const int MOD=1e9+7, M[2]={(int)1e9+9, (int)1e9+7}, P[2]={37, 41};
ar<int, 2> getHash(string s) {
ar<int, 2> res;
for (int i=0; i<2; ++i) {
ll pp=1, hsh=0;
for (char c : s) {
hsh=(hsh+(c-'a'+1)*pp)%M[i];
pp=pp*P[i]%MOD;
}
res[i]=hsh;
}
return res;
}
int n, k;
string name[50][1500];
map<ar<int, 2>, int> dp, last;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
for (int i=0; i<n; ++i) for (int j=0; j<k; ++j) cin >> name[i][j];
for (int i=0; i<k; ++i) ++dp[getHash(name[0][i])];
for (int i=1; i<n; ++i) { //current string is of length i+1
swap(dp, last);
dp.clear();
for (int j=0; j<k; ++j) {
ar<int, 2> cur=getHash(name[i][j]);
ar<int, 2> hsh=getHash(name[i][j].substr(0, i));
auto it=last.find(hsh);
if (it!=last.end()) dp[cur]=(dp[cur]+it->second)%MOD;
ar<int, 2> hsh2=getHash(name[i][j].substr(1));
if (hsh!=hsh2) {
hsh=hsh2;
it=last.find(hsh);
if (it!=last.end()) dp[cur]=(dp[cur]+it->second)%MOD;
}
}
//for (auto& x : dp) {cout << x.first << " " << x.second << "\n";}
//for (auto& x : dp) if (x.second>=MOD) x.second-=MOD;
//cout << "\n\n";
}
int ans=0;
for (auto& x : dp) ans=(ans+x.second)%MOD;
cout << ans << "\n";
return 0;
}
