#include <fstream>

using namespace std;
ifstream cin ("secv2.in");
ofstream cout ("secv2.out");
int v[50005],minn[5005], maxx=0;
int main()
{
    int n, k;
    cin >> n >> k;
    for(int i=1;i<=n;i++) {
        cin >> v[i];
        v[i]+=v[i-1];
        minn[i]=min(minn[i-1],v[i]);
    }
    for(int i=k;i<=n;i++) {
        maxx=max(v[i]-minn[i-k+1]);
    }
    cout << maxx;
    return 0;
}