/*
COCI 2020 Trener
- Notice that we only need to check consecutive words and that only the first and last
letters can differ
- We just use a map and some dp to solve this
- Complexity: O(NK^2)
*/
#include <bits/stdc++.h>
#define FOR(i, x, y) for (int i = x; i < y; i++)
typedef long long ll;
using namespace std;
const ll M = 1e9 + 7;
ll dp[1501];
map<string, ll> mp;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, k;
cin >> n >> k;
FOR(i, 1, n + 1) FOR(j, 1, k + 1) {
string s;
cin >> s;
dp[j] = (i > 1 ? mp[s.substr(0, i - 1)] + mp[s.substr(1, i - 1)] : 1);
if (i > 1 && s.substr(0, i - 1) == s.substr(1, i - 1)) dp[j] -= mp[s.substr(1, i - 1)];
if (dp[j] >= M) dp[j] -= M;
mp[s] += dp[j];
if (mp[s] >= M) mp[s] -= M;
}
ll ans = 0;
FOR(i, 1, k + 1) {
ans += dp[i];
if (ans >= M) ans -= M;
}
cout << ans;
return 0;
}
