#include<iostream>
#include<fstream>

using namespace std;

const int inf = 1e9 + 5;
const int MAXN = 1e5 + 5;

int n, k;
int a[MAXN];

int prefix[MAXN];
int zeroCount[MAXN];

struct node
{
    int l, r;
    int maxValue;

    node *L, *R;

    node(int l, int r)
    {
        this->l = l;
        this->r = r;

        this->L = nullptr;
        this->R = nullptr;
    }

    void build(int l, int r)
    {
        if(l==r)
        {
            this->maxValue = prefix[l];
            return;
        }

        this->L = new node(l, (l+r)/2);
        this->R = new node((l+r)/2+1, r);

        this->L->build(l, (l+r)/2);
        this->R->build((l+r)/2+1, r);

        this->maxValue = max(this->L->maxValue, this->R->maxValue);
    }

    int query(int ql, int qr)
    {
        if(this->l>=ql && this->r<=qr) return this->maxValue;
        if(this->r<ql || this->l>qr) return -inf;

        return max(this->L->query(ql, qr), this->R->query(ql, qr));
    }
};

node *T;
int getZeros(int l, int r)
{
    if(l==0) return zeroCount[r];
    return zeroCount[r] - zeroCount[l-1];
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    ifstream cin("krasi.in");
    ofstream cout("krasi.out");

    int answer = -inf;

    cin >> n >> k;
    for(int i = 0;i<n;i++)
    {
        cin >> a[i];
    }

    zeroCount[0] = ((a[0]==0)?1:0);
    for(int i = 1;i<n;i++)
    {
        zeroCount[i] = zeroCount[i-1] + ((a[i]==0)?1:0);
    }

    prefix[0] = a[0];
    for(int i = 1;i<n;i++)
    {
        prefix[i] = prefix[i-1] + a[i];
    }

    T = new node(0, n-1);
    T->build(0, n-1);

    for(int i = 0;i<n;i++)
    {
        int index;
        int l, r, mid;

        l = i;
        r = n - 1;
        while(l+1<r)
        {
            mid = (l+r)/2;

            if(getZeros(i, mid)<=k) l = mid;
            else r = mid - 1;
        }

        if(getZeros(i, r)<=k) index = r;
        else index = l;

        int current = T->query(i, index);
        if(i!=0) current -= prefix[i-1];

        answer = max(answer, current);
    }

    cout << answer << '\n';
}