#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 2000000000000000005

int check(string &a,string &b){
	bool f0 = true,f1 = true;
	rep(i,a.size()){
		if(a[i]<b[i])f0 = false;
		if(a[i]>b[i])f1 = false;
	}
	if(f0)return 1;
	if(f1)return -1;
	return 0;
}

int main(){
	
	int N,K;
	cin>>N>>K;
	
	vector<string> ans;
	rep(i,N){
		string t;
		cin>>t;
		//rep(j,K)scanf("%d",&t[j]);
		bool f = true;
		rep(j,ans.size()){
			if(ans[j]==t)f = false;
		}
		if(!f)continue;
		{
			vector<string> na;
			rep(j,ans.size()){
				if(check(t,ans[j])==1)continue;
				na.push_back(ans[j]);
				if(check(t,ans[j])==-1)f = false;
			}
			if(f)na.push_back(t);
			swap(ans,na);
		}
	}
	cout<<N-ans.size()<<endl;
			
	
    return 0;
}