#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;
struct HASH{
int sz = 2;
int p[2] = {29,31};
array < int , 2 > get(string &str){
array < int , 2 > ret,kat;
ret[0] = ret[1] = 0;
kat[0] = kat[1] = 1;
for(auto itr : str){
for(int i = 0;i<sz;i++) {
ret[i] = (ret[i] + kat[i] * (itr - 'a' + 1)) % mod;
kat[i] = (kat[i] * p[i]) % mod;
}
}
return ret;
}
} h;
void solve(){
int n,k;cin >> n >> k;
string v[n+1][k];
map < array < int , 2 > , vector < int > > mpa;
for(int i = 1;i<=n;i++){
for(int j = 0;j<k;j++){
cin >> v[i][j];
mpa[h.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[h.get(s1)];
vector < int > ind2 = mpa[h.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();
}
