n,d=map(int,input().split())
x=y=0
for i in range(d):
if '0' in input():
x+=1
else:
x=0
y=max(x,y)
print(y)#include <bits/stdc++.h>
using namespace std;
int main(){
int n,d;
cin>>n>>d;
int count = 0;
int maxcount = 0;
bool contin = true;
string a;
for(int i = 0;i<d;i++){
cin>>a;
for(int i = 0;i<n;i++){
if(a[i] != '1'){
contin = false;
break;
}
}
if(!contin){
count++;
}else{
maxcount = max(count,maxcount);
count = 0;
}
contin = true;
}
maxcount = max(count,maxcount);
cout<<maxcount<<endl;
}1333A - Little Artem | 432D - Prefixes and Suffixes |
486A - Calculating Function | 1373B - 01 Game |
1187A - Stickers and Toys | 313B - Ilya and Queries |
579A - Raising Bacteria | 723A - The New Year Meeting Friends |
302A - Eugeny and Array | 1638B - Odd Swap Sort |
1370C - Number Game | 1206B - Make Product Equal One |
131A - cAPS lOCK | 1635A - Min Or Sum |
474A - Keyboard | 1343A - Candies |
1343C - Alternating Subsequence | 1325A - EhAb AnD gCd |
746A - Compote | 318A - Even Odds |
550B - Preparing Olympiad | 939B - Hamster Farm |
732A - Buy a Shovel | 1220C - Substring Game in the Lesson |
452A - Eevee | 1647B - Madoka and the Elegant Gift |
1408A - Circle Coloring | 766B - Mahmoud and a Triangle |
1618C - Paint the Array | 469A - I Wanna Be the Guy |