// 愚直解

#include <stdio.h>
#define MAX_N 100000
#define MAX_K 10

#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma warning(disable: 4996)


int main(void) {
	int N, K;	scanf("%d", &N);	scanf("%d", &K);
	char s[MAX_N][MAX_K];
	for (int i = 0; i < N; ++i) {
		scanf("%s", s[i]);
	}

	int local_max[MAX_N];
	for (int i = 0; i < N; ++i) {
		local_max[i] = 1;
	}
	for (int i = 0; i < N - 1; ++i) {
		for (int j = i + 1; j < N; ++j) {
			int flag = 1;
			for (int k = 0; k < K; ++k) {
				if (s[i][k] <= s[j][k]) {
					continue;
				}
				flag = 0;
				break;
			}
			if (flag == 1) {
				local_max[j] = 0;
				continue;
			}

			flag = 1;
			for (int k = 0; k < K; ++k) {
				if (s[i][k] >= s[j][k]) {
					continue;
				}
				flag = 0;
				break;
			}
			if (flag == 1) {
				local_max[i] = 0;
				continue;
			}
		}
	}

	int ans = N;
	for (int i = 0; i < N; ++i) {
		ans -= local_max[i];
	}
	printf("%d\n", ans);

	return 0;
}