#include <iostream>
#include<fstream>
using namespace std;
fstream f("transport.in",ios::in);
fstream g("transport.out",ios::out);
long long i,l,j,n,a,max2=0,b[16001],k,s,max1;
int main()
{f>>n>>k;
for(l=1;l<=n;l++)
  {f>>b[l];
  s=s+b[l];}
  max1=b[1];
for(i=1;i<=n;i++)
 { if(max1<(s/k+k/2))
    max1=max1+b[i];
    else{
    if(max2<max1)
    max2=max1;
    max1=0;
    }
 }
 g<<max2;


    return 0;
}