#include<iostream>
using namespace std;
int main()
{
int n;
int a[110000];
int cnt = 1;
int m = 0,k=0;
cin >> n;
for(int i = 1; i <= n; i++)
{
cin >> a[i];
if(a[i] == 1)
{
k = k + 1;
}
}
if(k == 0)
{
cout << k;
return 0;
}
for(int i = 1; i <= n; i++)
{
if(a[i] == 1 && a[i + 1] == 1)
{
cnt = cnt + 1;
}
else
{
m = max(m,cnt);
cnt = 1;
}
}
cout << m;
return 0;
}
