#include<bits/stdc++.h>

using namespace std;

#define pb push_back

const int maxi=1e6+10;

int a[maxi];
vector<int> v[maxi];
int n,k;
long long s[maxi];
int zero[maxi];
multiset<long long> ms;
long long ans;

void read()
{
    freopen("krasi.in","r",stdin);
    cin>>n>>k;

    for (int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        s[i]=s[i-1]+a[i];
        zero[i]=zero[i-1];
        if (!a[i])
            zero[i]++;
    }


    fclose(stdin);
}

void solve()
{
     int l=0;
     int r=1;

     ms.insert(0);
     while(r<=n)
     {
             while(zero[r]-zero[l]>k)
             {
                 ms.erase(ms.find(s[l]));
                 l++;
             }

         ans = max (ans, s[r]-*ms.begin());
         ms.insert(s[r]);
         r++;
     }
}
void print()
{
    freopen("krasi.out","w",stdout);
    printf("%lld\n",ans);
   fclose(stdout);
}
int main()
{
   read();
   solve();
   print();
   return 0;
}