#include <bits/stdc++.h>
using namespace std;
#define SZ(x) (int)(x).size()
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define RFOR(i,a,b) for (int i=(a);i>=(b);--i)
const int MX_N = 55;
const int MX_K = 1505;
const int MOD = 1e9+7;
const int P = 101, Q = 1e9+7;
int N, K;
string S[MX_N][MX_K];
pair<int,int> h[MX_N][MX_K];
int dp[MX_N][MX_K];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cin >> N >> K;
FOR(i,1,N){
FOR(j,1,K) cin >> S[i][j];
}
FOR(j,1,K) {
int cur = 0;
FOR(k,0,N-2) {
cur = ((1LL*cur*P) % Q + S[N][j][k]-'a') % Q;
}
h[N][j].first = cur;
cur = 0;
FOR(k,1,N-1) {
cur = ((1LL*cur*P) % Q + S[N][j][k]-'a') % Q;
}
h[N][j].second = cur;
dp[N][j] = 1;
}
RFOR(i,N-1,1){
FOR(j,1,K){
dp[i][j] = 0;
int cur = 0;
FOR(k,0,i-2) {
cur = ((1LL*cur*P) % Q + S[i][j][k]-'a') % Q;
}
h[i][j].first = cur;
cur = ((1LL*cur*P) % Q + S[i][j][i-1]-'a') % Q;
//cout << "i j " << i << " " << j << " :: " << cur << endl;
FOR(k,1,K) {
if (cur == h[i+1][k].first || cur == h[i+1][k].second) {
//cout << i << " " << j << " :: " << i+1 << " " << k << endl;
dp[i][j] += dp[i+1][k];
if (dp[i][j] >= MOD) dp[i][j] -= MOD;
}
}
cur = 0;
FOR(k,1,i-1) {
cur = ((1LL*cur*P) % Q + S[i][j][k]-'a') % Q;
}
h[i][j].second = cur;
}
}
int ans = 0;
FOR(i,1,K){
ans += dp[1][i];
if (ans >= MOD) ans -= MOD;
}
cout << ans << '\n';
}
