#pragma comment(linker, "/STACK:60777216")  

#include <cassert>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<complex>
#include<vector>
#include<cstring>
#include<set>
#include<map>
#include<cmath>
#include<queue>
#include<string>
#include<cstdlib>
#include<memory.h>
#include<ctime>
#include<bitset>
#include<fstream>
#include<queue>
#include<stack>
#include<unordered_map>
#include<unordered_set>

using namespace std;

typedef long double ld;

typedef long long ll;
typedef pair<int,int>	pii;
typedef pair<ld,ld>	pdd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef pair<ll,ll> pl;

#define FOR(i,a,b)		for(int i=(a);i<(b);i++)	
#define REP(i,n)		FOR(i,0,n)
#define SORT(v)			sort((v).begin(),(v).end())
#define UN(v)			SORT(v),(v).erase(unique((v).begin(),(v).end()),(v).end())
#define CL(a,b)			memset(a,b,sizeof a)
#define pb				push_back

int n,k;
int a[111111];

int solve(vi& a){
	int sum = 0;
	int res = 0;
	REP(i,a.size()){
		sum+=a[i];
		if(sum<0)sum=0;
		res = max(res, sum);
	}
	return res;
}
int getsum(vi& a){
	int x = 0;
	REP(i,a.size()) x+=a[i];
	return x;
}
int getbeg(vi& a){
	int best = 0;
	int sum = 0;
	REP(i,a.size()){
		sum += a[i];
		best=max(best,sum);
	}
	return best;
}

int eend[111111];
int beg[111111];
int all[111111];

int main(){	
#ifdef LocalHost
	freopen("input.txt","r",stdin);
	//freopen("output.txt","w",stdout);
#endif
#ifndef LocalHost
	freopen("krasi.in","r",stdin);
	freopen("krasi.out","w",stdout);
#endif

	cin>>n>>k;
	REP(i,n)scanf("%d",a+i);

	vector<vi> b;
	vi t;
	REP(i,n){
		if(a[i]==0){
			b.pb(t);
			t.clear();
		}else{
			t.pb(a[i]);
		}
	}
	if(!t.empty()) b.pb(t);
	int res = 0;
	REP(i,b.size()){
		res=max(res,solve(b[i]));
		all[i] = getsum(b[i]);
		eend[i] = getbeg(b[i]);
		reverse(b[i].begin(),b[i].end());
		beg[i] = getbeg(b[i]);
	}
	REP(i,b.size()){
		int sum = beg[i];
		for(int j = i + 1; j < min(i+k+1,(int)b.size());j++){
			res=max(res,sum+eend[j]);
			sum += all[j];
		}
	}
	cout<<res<<endl;

#ifdef LocalHost
	printf("TIME: %.3lf\n",ld(clock())/CLOCKS_PER_SEC);
#endif
	return 0;
}