#include <bits/stdc++.h>
#define ST first
#define ND second
#define PB push_back
using namespace std;
using ll = long long;
using pi = pair<int,int>;
using vi = vector<int>;
const int mod = 1e9 + 7, p = 31;
int n, k;
map<int,int>opt, opt2;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
for(int i = 0; i < n; ++i) {
for(int j = 0; j < k; ++j) {
string s;
cin >> s;
int h = 0;
int h2 = 0;
int h3 = 0;
for(auto c : s) {
h2 = h;
if(h != 0) {
h3 = ((ll)h3 * p + (c - 'a' + 1)) % mod;
}
h = ((ll)h * p + (c - 'a' + 1)) % mod;
}
//cout << h << " " << h2 << " " << h3 << "\n";
if(i == 0) {
opt2[h]++;
} else {
opt2[h] = (opt2[h] + opt[h2]) % mod;
if(h3 != h2)
opt2[h] = (opt2[h] + opt[h3]) % mod;
}
}
opt.swap(opt2);
opt2.clear();
}
int ans = 0;
for(auto it : opt) {
ans = (ans + it.ND) % mod;
}
cout << ans;
}
