// author: erray
#include <bits/stdc++.h>
#ifdef DEBUG
#include "debug.h"
#else
#define debug(...) void(37)
#endif
using namespace std;
constexpr int md = int(1e9) + 7;
int add(int x, int y) {
if ((x += y) >= md) {
x -= md;
}
return x;
}
int mul(int x, int y) {
return 1LL * x * y % md;
}
constexpr int base = 31;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
array<int, 26> hv{};
iota(hv.begin(), hv.end(), 0);
random_shuffle(hv.begin(), hv.end());
int N, K;
cin >> N >> K;
vector<vector<string>> S(N, vector<string>(K));
for (int i = 0; i < N; ++i) {
for (int j = 0; j < K; ++j) {
cin >> S[i][j];
}
}
map<int, int> ans;
for (int i = 0; i < N; ++i) {
map<int, int> next_ans;
for (int j = 0; j < K; ++j) {
int h = 0, L = -1;
for (int k = 0; k <= i; ++k) {
h = mul(h, base);
h = add(h, hv[S[i][j][k] - 'a']);
if (k == i - 1) {
L = h;
}
}
int R = 0;
for (int k = 1; k <= i; ++k) {
R = mul(R, base);
R = add(R, hv[S[i][j][k] - 'a']);
}
int res = (i == 0);
res = add(res, ans[L]);
if (R != L) {
res = add(res, ans[R]);
}
next_ans[h] = add(next_ans[h], res);
}
swap(ans, next_ans);
}
int p = 0;
for (auto[foo, x] : ans) {
p = add(p, x);
}
cout << p << '\n';
}
