#include<bits/stdc++.h>
#define endl '\n'
using namespace std;
const int MAXN = 55, MAXK = 1510;
const long long mod = 1e9 + 7;
int n, k;
long long dp[MAXN][MAXK];
string s[MAXN][MAXK];
int main()
{
ios_base::sync_with_stdio(NULL);
cin.tie(NULL);
cout.tie(NULL);
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 = 1; i < n; i ++)
for (int j = 1; j <= k; j ++)
for (int d = 1; d <= k; d ++)
{
string s1 = s[i][j], s2 = s[i + 1][d].substr(0, s[i + 1][d].size() - 1), s3 = s[i + 1][d].substr(1, s[i + 1][d].size() - 1);
if (s1 == s2 || s1 == s3)
dp[i + 1][d] = (dp[i + 1][d] + dp[i][j]) % mod;
}
long long ans = 0;
for (int j = 1; j <= k; j ++)
ans = (ans + dp[n][j]) % mod;
cout << ans << endl;
return 0;
}
