// Author: Ngo Ba Van
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
using ii=pair<ll,ll>;
const ll N=1e3+5,M=1e9+7;
ll n,res,dp[N][N],k;
map<string,ll>m[2];
string s;
void nhap()
{
cin>>n>>k; int a=0,b=1;
m[0][""]=1;
for (int i=1;i<=n;i++)
{
for (int j=1;j<=k;j++)
{
res=0;
cin>>s; string t1,t2;
t1=s.substr(0,s.size()-1);
t2=s.substr(1,s.size()-1);
if (m[a].count(t1)) res=(res+m[a][t1])%M;
if (t1!=t2)
{
if (m[a].count(t2)) res=(res+m[a][t2])%M;
}
m[b][s]=(m[b][s]+res)%M;
}
swap(a,b);
m[b].clear();
}
res=0;
for (auto i:m[a])
res=(res+i.se)%M;
cout<<res%M;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
#define task "a"
//define task ""
int t=1;
//cin>>t;
while (t--)
nhap();
}
