#include<fstream>
#include<utility>
using namespace std;

void read();
void write();
void comp();
bool test(int v);

int n, m, mx;
char a[1005][1005], b[1005][1005];
pair<int, int> dr[1000001];

int main()
{
	read();
	comp();
	write();
	return 0;
}

void read()
{
	ifstream fin("barbar.in");
	fin >> n >> m;
	for (int i = 0; i < n; ++i)
	{
		fin >> a[i];
		
	}
	fin.close();
}

void write()
{
	ofstream fout("barbar.out");
	fout << mx;
	fout.close();
}

void comp()
{
	int l1 = 0, l2 = 1000;
	while (l1 <= l2)
	{
		int mid = (l1 + l2) >> 1;
		if (test(mid))
		{
			mx = mid;
			l1 = mid + 1;
		}
		else
			l2 = mid - 1;
	}
}