#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define int long long
const int mod = 1e9 + 7;
inline long long get(string const& s) {
const int p = 29;
const int m = 1e9 + 7;
long long hash_value = 0;
long long p_pow = 1;
for (char c : s) {
hash_value = (hash_value + (c - 'a' + 1) * p_pow) % m;
p_pow = (p_pow * p) % m;
}
return hash_value;
}
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
// http://xorshift.di.unimi.it/splitmix64.c
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
void solve(){
int n,k;cin >> n >> k;
string v[n+1][k];
unordered_map < int , vector < int > , custom_hash > mpa;
for(int i = 1;i<=n;i++){
for(int j = 0;j<k;j++){
cin >> v[i][j];
mpa[get(v[i][j])].push_back(j);
}
}
int dp[n+1][k];
memset(dp , 0 , sizeof(dp));
for(int i = 0;i<k;i++)dp[1][i] = 1;
for(int i = 2;i<=n;i++){
for(int j = 0;j<k;j++){
string s1 = string(v[i][j].begin() , v[i][j].end()-1) , s2 = string(v[i][j].begin()+1 , v[i][j].end());
vector < int > ind1 = mpa[get(s1)];
vector < int > ind2 = mpa[get(s2)];
for(auto itr : ind2)ind1.push_back(itr);
sort(ind1.begin(),ind1.end());
ind1.resize(unique(ind1.begin() , ind1.end()) - ind1.begin());
for(auto itr : ind1){
dp[i][j] = (dp[i][j] + dp[i-1][itr]) % mod;
}
}
}
int ans = 0;
for(int i = 0;i<k;i++)ans = (ans + dp[n][i]) % mod;
cout << ans << endl;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);
int testcase = 1;//cin >> testcase;
while(testcase--)solve();
}
