#include<bits/stdc++.h>

using namespace std;

/// Typedef
typedef long long ll;

#define sc1(a) scanf("%lld",&a)
#define sc2(a,b) scanf("%lld %lld",&a,&b)

#define pf1(a) printf("%lld\n", a)
#define pf2(a,b) printf("%lld %lld\n",a,b)

int main() {

    //seive();
    //preCal();

    ll tc, num, t = 1, choose;

    //freopen("/opt/Coding/clion code/input.txt", "r", stdin);
    //freopen("/opt/Coding/clion code/output.txt", "w", stdout);

    sc1(num);

    ll arr[num * 2];

    for(ll i = 0; i < num; i++){
        sc1(arr[i]);
        arr[i + num] = arr[i];
    }


    ll cnt = 0, ans = 0;

    for(ll i = 0; i < 2 * num; i++){
        if(arr[i] == 1) cnt++;
        else cnt = 0;
        ans = max(ans, cnt);
    }

    pf1(ans);

    return 0;
}