#include <bits/stdc++.h>
typedef long long ll;
#define FOR(i,a,b) for(int i = a;i < b;i ++)
#define sz(a) int((a).size())
#define trav(a, b) for(auto a : b)
#define mk make_pair
#define f first
#define s second
#define pb push_back
using namespace std;
ll modF = 1e9 + 7;
#define RANDOM chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()
ll mult(ll a,ll b){return (a * b) % modF;}
ll add(ll a,ll b){return (a + b) % modF;}
ll sub(ll a,ll b){return (a - b + modF) % modF;}
struct hassh{
ll h1,h2;
hassh():hassh(0,0){}
hassh(ll h,ll hh):h1(h),h2(hh){}
bool operator<(const hassh& b) const {
if(h1 == b.h1)return h2 < b.h2;
return h1 < b.h1;
}
bool operator==(const hassh& b) const {
if(h1 == b.h1 and h2 == b.h2) return true;
return false;
}
};
ll b1 = (RANDOM) % modF;
ll b2 = (RANDOM) % modF;
struct StringHash{
ll N;
vector<ll> pw1, pw2;vector<hassh> hsh;
StringHash(){}
StringHash(const string& s){
N = sz(s);
hsh.assign(N,hassh(0,0));pw1.assign(N + 1,1);pw2.assign(N + 1,1);
FOR(i,1,N + 1){
pw1[i] = mult(b1, pw1[i - 1]);
pw2[i] = mult(b2, pw2[i - 1]);
}
FOR(i,0,N){
if(i == 0){
hsh[i].h1 = s[i];hsh[i].h2 = s[i];
} else {
hsh[i].h1 = add(mult(hsh[i - 1].h1, b1), s[i]);hsh[i].h2 = add(mult(hsh[i - 1].h2, b2), s[i]);
}
}
}
hassh find_hash(ll l,ll r){
ll H1 = hsh[r].h1, H2 = hsh[r].h2;
if(l != 0){
H1 = sub(H1, mult(hsh[l - 1].h1, pw1[r - l + 1])), H2 = sub(H2, mult(hsh[l - 1].h2, pw2[r - l + 1]));
}
return hassh(H1,H2);
}
};
int main(){
ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int n, k;
cin >> n >> k;
vector<vector<string>> a(n, vector<string>(k));
vector<vector<StringHash>> sh(n, vector<StringHash>(k));
for(int i = 0;i < n;i ++){
for(int j = 0;j < k;j ++){
cin >> a[i][j];
sh[i][j] = StringHash(a[i][j]);
}
}
ll dp[n][k];
ll ans = 0;
for(int i = 0;i < n;i ++){
for(int j = 0;j < k;j ++){
dp[i][j] = 0;
if(i == 0){
dp[i][j] = 1;
} else {
for(int it = 0;it < k;it ++){
if(sh[i][j].find_hash(0, i - 1) == sh[i - 1][it].find_hash(0,i - 1) or sh[i][j].find_hash(1, i) == sh[i - 1][it].find_hash(0,i - 1)){
dp[i][j] = (dp[i][j] + dp[i - 1][it]) % modF;
}
}
}
if(i == n - 1)ans = (ans + dp[i][j]) % modF;
}
}
printf("%lld\n", ans);
return 0;
}
