#include <bits/stdc++.h>
using namespace std;
#define eb emplace_back
#define pb push_back
#define ppb pop_back
#define ub upper_bound
#define lb lower_bound
#define bs binary_search
#define cln(a,s) memset((a),0,sizeof((a)[0])*(s))
#define all(x) (x).begin() , (x).end()
#define fi first
#define se second
#define int int
using pii = pair<int,int>;
using ll = long long;
const int maxn = 55;
const int maxk = 1505;
const int inf = 1e9;
const int mod = 1e9+7;
int n,k;
string a[maxn][maxk];
int dp[maxn][maxk];
int32_t main () {
//freopen("in","r",stdin); freopen("out","w",stdout);
ios_base::sync_with_stdio(0); cout.tie(0); cin.tie(0);
cin >> n >> k;
for(int i=1;i<=n;i++)
for(int j=1;j<=k;j++)
cin >> a[i][j];
for(int i=1;i<=k;i++) dp[1][i] = 1;
for(int i=2;i<=n;i++)
for(int j=1;j<=k;j++) {
string sub1 = a[i][j].substr(0,i-1);
string sub2 = a[i][j].substr(1,i-1);
for(int m=1;m<=k;m++)
if(a[i-1][m] == sub1 or a[i-1][m] == sub2) {
dp[i][j] += dp[i-1][m];
dp[i][j] %= mod;
}
}
int ans = 0;
for(int i=1;i<=k;i++) {
ans += dp[n][i];
ans %= mod;
}
cout << ans << endl;
}
