#include<bits/stdc++.h>
#define cin fin
#define cout fout
using namespace std;
ifstream fin("secv2.in");
ofstream fout("secv2.out");
int n,k,s[100005],mx[100005];
int main(){
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        int x;
        cin>>x;
        s[i]=s[i-1]+x;///vector de sume partiale
    }
    mx[n+1]=-1e9;///maximul din partea dreapta
    for(int i=n;i>=1;i--)///de la dreapta la stanga
        mx[i]=max(mx[i+1],s[i]);///maximul de pe toate prefixele
    int r=-1e9;///raspunsul
    for(int i=0;i<=n-k;i++){
        r=max(r,mx[i+k]-s[i]);
    }
    cout<<r;
    return 0;
}