#include<bits/stdc++.h>
#define fi first
#define se second
using namespace std;
const int MOD=1e9+7;
map<string,int> dp;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int n,k;
cin>>n>>k;
long long ans=0;
dp[""]=1;
for(int i=1;i<=n;i++)
{
for(int j=1;j<=k;j++)
{
string s;
cin>>s;
if(i==n)
ans=(ans-dp[s])%MOD;
string s1=s,s2=s;
s1.pop_back();
s2.erase(s2.begin());
dp[s]=((long long)dp[s]+dp[s1]+(s1!=s2)*dp[s2])%MOD;
if(i==n)
ans=(ans+dp[s])%MOD;
}
}
cout<<(ans+MOD)%MOD<<"\n";
return 0;
}
