#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

vector<string> s;
int ans = 0;
int n,m;

void dfs(vector<int> &t,int cur){
	//cout<<cur<<endl;
	if(cur==m+1){
		ans++;
		return;
	}
	rep(i,26){
		int M = 0;
		char c = 'a';
		c += i;
		auto tt = t;
		rep(j,n){
			if((cur==m&&t[j]==0) || s[j][cur-t[j]]!=c){
				t[j]++;
				M = max(M,t[j]);
				if(M>=2)break;
			}
		}
		//cout<<cur<<','<<i<<','<<M<<endl;
		if(M<=1){
			dfs(t,cur+1);
		}
		t = tt;
	}
}

int main(){
	
	
	cin>>n>>m;
	s.resize(n);
	rep(i,n)cin>>s[i];
	
	vector<int> t(n,0);
	dfs(t,0);
	cout<<ans<<endl;
	
	return 0;
}