#include<iostream>
#include <fstream>
using namespace std;
int lengthOfArr,brNulls;
int arr[100000],sum1=0,maxSum=0;
void Input()
{
	ifstream InputFile;
	InputFile.open("krasi.in",ios::in);
	InputFile>>lengthOfArr>>brNulls;
	for(int i=0;i<lengthOfArr;i++)
	{
		InputFile>>arr[i];
	}
	
}
void Output()
{
	ofstream OutputFile;
	OutputFile.open("krasi.out",ios::out);
	OutputFile<<maxSum;
	
}
int main()
{
	Input();
	int count=0,arrOfNulls[100000],sum[100000],counter=0;
	int j1=0,start;
	for(int i=0;i<lengthOfArr;i++)
	{
		if(arr[i]==0)
		{
		    arrOfNulls[j1]=i;
		    j1++;	
		}
	}
	for(int i=0;i<j1;i++)
	{
		start=count;
		count=arrOfNulls[i];
		for	(int j=start;j<count;j++)
		{
			sum[i]+=arr[j];
		}
	}
	for(int i=0;i<j1;i++)
	{
		sum1=0;
		for(int k=i;j1;k++)
		{if(k+1==brNulls)
			break;
			sum1+=sum[k];
			
		}
		if(maxSum<sum1)
		{
			maxSum=sum1;
		}
	}
	Output();
}