#include<bits/stdc++.h>
#define int long long
typedef long long ll;
using namespace std;
const int N = 2e3 + 10;
const int mod = 1e9 + 7;
void solve(){
int n,m;
cin>>n>>m;
vector<int> a(n+1,0),sum(n+1,0);
for (int i = 1; i <= n; ++i) {
cin>>a[i];
sum[i] = sum[i-1] + a[i];
}
int maxx = 0;
deque<int> dq; //用来维护i-m+1 -- i-1的sum最小值
dq.push_back(0);
for (int i = 1; i <= n; ++i) {
if(!dq.empty() && dq.front() < i - m)
dq.pop_front();
while (!dq.empty() && sum[i] <= sum[dq.back()]){
dq.pop_back();
}
dq.push_back(i);
if (dq.size())maxx = max(maxx,sum[i] - sum[dq.front()]);
}
cout<<maxx<<endl;
}
signed main(){
ios::sync_with_stdio(false);
cin.tie(NULL),cout.tie(NULL);
int t = 1;
//cin>>t;
while(t--){
solve();//1 2 3 4 5
}
return 0 ;
}