#include <iostream>
using namespace std;
int main() {
// your code goes here
int n,k;
cin>>n>>k;
int a[n],i,max,pos;
for(i=0;i<n;i++){
cin>>a[i];
}
for(i=1;i<n;i++){
a[i] += a[i-1];
}
/* for(i=0;i<n;i++){
cout << a[i]<<" ";
}*/
if(k>=n){
max = a[n-1];
cout<<max;
}else{
max = a[k-1],pos=0;
// cout<<max<<" ";
for(i=1;i<=n-k;i++){
if(a[i+k-1]-a[i-1] > max){
max = a[i+k-1]-a[i-1];
pos = i;
}
}
// cout<<max<<" ";
if(k>=n-k){
if(pos>0){
max += a[pos-1];
if(pos < n-k){
max += (a[n-1]-a[pos+k-1]);
}
}else{
max += (a[n-1]-a[pos+k-1]);
}
cout<<max;
}else{
int j = pos,max1=max;
//cout<<max1<<" ";
for(i=pos+k;i<n;i++){
a[j] = a[i]-(a[pos+k-1]-a[pos-1]);
j++;
}
/* for(i=0;i<j;i++){
cout<<a[i]<<" ";
}*/
max = a[k-1],pos=0;
// cout<<max<<" ";
for(i=1;i<=j-k;i++){
if(a[i+k-1]-a[i-1] > max){
max = a[i+k-1]-a[i-1];
pos = i;
// cout<<pos<<" ";
}
}
// cout<<max<<" ";
max1 +=max;
max = max1;
cout<<max;
}
}
return 0;
}
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