#include <bits/stdc++.h>
//#pragma GCC optimize("unroll-loops")
//#pragma GCC optimize("-O3")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("fast-math")
//#pragma GCC optimize("no-stack-protector")
#define F first
#define S second
#define sz(x) ll(x.size())
#define pb push_back
#define N 75005
#define M ll(1e9 + 7)
using namespace std;
typedef long double ld;
typedef long long ll;
typedef short int si;
map <string, ll> dpl, dp;
int main()
{
ios_base::sync_with_stdio(0); istream::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n, k;
cin >> n >> k;
vector <string> b(k);
dp.clear(); dpl.clear();
for (register int i = 0; i < k; i++) {string str; cin >> str; dpl[str]++;}
for (register int i = 1; i < n; i++)
{
for (register int j = 0; j < k; j++)
{
string str1, str2;
cin >> b[j];
str1 = b[j].substr(0, i);
str2 = b[j].substr(1);
ll sm = dpl[str1];
if (str1 != str2) sm = (sm + dpl[str2]);
dp[b[j]] = (dp[b[j]] + sm);
}
dpl = dp;
dp.clear();
}
ll ans = 0;
for (register int i = 0; i < k; i++) ans = (ans + dpl[b[i]]) % M;
cout << ans << endl;
}
