#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
using namespace std;
//#define int long long
const int MOD = 1e9 + 7;
#define ONLINE_JUDGE
#ifndef ONLINE_JUDGE
#define OPEN freopen(".in", "r", stdin); \
freopen(".out", "w", stdout);
#else
#define OPEN void(23);
#endif
string arr[55][1505];
bool check(string &a, string &b)
{
int n = b.size();
bool ok = true;
for(int i = 1; i <= n -1; i++)
{
ok &= a[i -1] == b[i -1];
}
if(ok) return true;
ok = true;
for(int i = 2; i <= n; i++)
{
ok &= a[i -2] == b[i -1];
}
return ok;
}
void solve()
{
int n, k; cin >> n >> k;
for(int i = 1; i <= n; i++)
for(int j = 1; j <= k; j++)
cin >> arr[i][j];
vector <int> dp(k +1, 1);
for(int i = 1; i <= n -1; i++)
{
vector <int> dp2(k +1);
for(int j = 1; j <= k; j++)
{
for(int c = 1; c <= k; c++)
{
if(check(arr[i][j], arr[i +1][c]))
dp2[c] = (dp2[c] + dp[j]) % MOD;
}
}
swap(dp, dp2);
}
int cev = 0;
for(int i = 1; i <= k; i++) cev = (cev + dp[i]) % MOD;
cout << cev;
return;
}
int32_t main()
{
OPEN;
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int t = 1; //cin >> t;
while(t--)
{
solve();
}
}
