#include <cstdio>
#include <iostream>
using namespace std;

char s[100][100];
int ans[100],sum[100][100],n,m;

int main(){
	freopen("skicourse.in","r",stdin);
	freopen("skicourse.out","w",stdout);
	cin >> n >> m;
	int i,j;
	for (i = 0; i < n; i++){
		cin >> s[i];
	}
	for (i = 0; i < n; i++){
		sum[i][0] = 1;
		for (j = 1; j < m; j++){
			if (s[i][j] == s[i][j-1]) sum[i][j] = sum[i][j-1]+1;
			else sum[i][j] = 1;
			if (sum[i][j] > ans[i]) ans[i] = sum[i][j];
		}
	}
	m = 0x3f3f3f3f;
	for (i = 0; i < n; i++)
		if (ans[i] < m) m = ans[i];
	if (m >= (n>>1) && m != n) m = n>>1;
	printf("%d",m);
	return 0;
}