// 愚直高速化　set<int> ver.

#include <bits/stdc++.h>
using namespace std;
using Int = long long;
constexpr static int mod = 1e9 + 7;
constexpr static int inf = (1 << 30) - 1;
constexpr static Int infll = (1LL << 61) - 1;
int Competitive_Programming = (ios_base::sync_with_stdio(false), cin.tie(nullptr), cout << fixed << setprecision(15), 0);

#pragma region Debug Template

template <typename A, typename B>
string to_string(pair<A, B> p);

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);

string to_string(const string &s)
{
	return '"' + s + '"';
}

string to_string(const char *s)
{
	return to_string((string)s);
}

string to_string(bool b)
{
	return (b ? "true" : "false");
}

string to_string(vector<bool> v)
{
	bool first = true;
	string res = "{";
	for (int i = 0; i < static_cast<int>(v.size()); i++)
	{
		if (!first)
		{
			res += ", ";
		}
		first = false;
		res += to_string(v[i]);
	}
	res += "}";
	return res;
}

template <size_t N>
string to_string(bitset<N> v)
{
	string res = "";
	for (size_t i = 0; i < N; i++)
	{
		res += static_cast<char>('0' + v[i]);
	}
	return res;
}

template <typename A>
string to_string(A v)
{
	bool first = true;
	string res = "{";
	for (const auto &x : v)
	{
		if (!first)
		{
			res += ", ";
		}
		first = false;
		res += to_string(x);
	}
	res += "}";
	return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p)
{
	return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}

template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p)
{
	return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}

template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p)
{
	return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T)
{
	cerr << " " << to_string(H);
	debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif
#pragma endregion

int main()
{
	int N, K;
	cin >> N >> K;
	vector<string> s(N);
	vector<int> d(N, -'0' * K);

	for (int i = 0; i < N; i++)
		cin >> s[i];

	vector<set<int>> st(40);

	sort(s.begin(), s.end(), [](string &a, string &b)
		 { 
		int ret1 = 0, ret2 = 0;
		for (int j = 0; j < a.size(); j++)
			ret1 += a[j], ret2 += b[j];
			return ret1 > ret2; });

	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < K; j++)
			d[i] += s[i][j];
		st[d[i]].insert(i);
	}

	// debug_out(s);
	// return 0;
	int ans = 0;

	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < d[i]; j++)
		{
			vector<int> del;
			for (auto &&l : st[j])
			{
				if (i == l)
					continue;
				int cnt = 0;
				for (int k = 0; k < K; k++)
					cnt += (s[i][k] >= s[l][k]);

				if (cnt == K)
				{
					del.emplace_back(l);
					ans++;
				}
			}
			for (auto &&l : del)
				st[j].erase(l);
		}
	}

	cout << ans << "\n";
}