#include <bits/stdc++.h>

using namespace std;

int main(){
	int n, m;
	cin >> m >> n;
	vector<string> v;

	vector<int> days(m, 1);

	for (int i = 0; i < n; i++){
		string s;
		cin >> s;
		for (int j = 0; j < m; j++){
		 	if (s[j] == '0'){
		 	 	days[i] = 0;
		 	}
		}
	}

	int curr = 0, mx = 0;
    for (int i = 0; i < m; i++){
     	if (days[i]){
     	 	mx = max(mx, curr);
     	 	curr = 0;
     	}else{
     	 	curr++;
     	}
    }
    mx = max(mx, curr);
    cout << mx;

 	return 0;
}