import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class Main implements Runnable { //Runnableを実装する
    public static void main(String[] args) {
        new Thread(null, new Main(), "", 16 * 1024 * 1024).start(); //16MBスタックを確保して実行
    }
    
    int dfs(char[][] str, char[] ans, int pos, int[] equiv) {
    	int ret=0;
    	if (pos==ans.length) return 1;
    	for (int i=0;i<26;++i) {
    		ans[pos]=(char)(i+'a');
    		int[] nequiv=Arrays.copyOf(equiv, equiv.length);
    		boolean ok=true;
    		for (int j=0;j<str.length;++j) {
    			if (equiv[j] < str[j].length && ans[pos]==str[j][equiv[j]]) ++nequiv[j];
    			ok &= (pos+1)-nequiv[j] <= 1;
    		}
    		if (ok) ret += dfs(str, ans, pos+1, nequiv);
    	}
    	return ret;
    }
	
	public void run() {
		Scanner sc=new Scanner(System.in);
		PrintWriter pw=new PrintWriter(System.out);
		
		int N=sc.nextInt();
		int M=sc.nextInt();
		char[][] str=new char[N][M];
		for (int i=0;i<N;++i) str[i]=sc.next().toCharArray();
		int[] equiv=new int[M];
		char[] ans=new char[M+1];
		pw.println(dfs(str, ans, 0, equiv));
		pw.close();
		
	}	
	
	void tr(Object ... o) {System.out.println(Arrays.deepToString(o));}
}