#include <bits/stdc++.h>
using namespace std;
struct Fast {Fast(){std::cin.tie(0);ios::sync_with_stdio(false);}} fast;
/* define */
#define FOR(I,X,Y) for(long long (I)=(X);(I)<(Y);(I)++)
#define REP(I,X,Y) for(long long (I)=(Y)-1;(I)>=(X);(I)--)
#define ALL(X) (X).begin(),(X).end()
#define pb push_back
#define COUNT(V,X) upper_bound((V).begin(),(V).end(),X)-lower_bound((V).begin(),(V).end(),X)
#define debug(x) cerr<<#x<<':'<<x<<endl;
#define DEBUG(v) cerr<<#v<<':';for(auto xXx:v)cerr<<xXx<<' ';cerr<<endl;
#define Yes(X) if(X){cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}
#define YES(X) if(X){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}
#define ctoi(C) (C-'0')
/* alias */
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vii = vector<vector<int>>;
using vl = vector<long long>;
using vll = vector<vector<long long>>;
using pi = pair<int,int>;
using pl = pair<long long,long long>;
template<typename T> using PQ = priority_queue<T>;
template<typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;
/* const */
const long long dx[] = {1,0,-1,0};
const long long dy[] = {0,1,0,-1};
const long long dx8[] = {1,1,0,-1,-1,-1,0,1};
const long long dy8[] = {0,1,1,1,0,-1,-1,-1};
const long long dx9[] = {1,1,0,-1,-1,-1,0,1,0};
const int INF = 1000000007;
const long long LINF = 1000000000000000007;
/* func */
template <typename T> inline bool chmin(T& a, const T& b) {if (a > b) a = b; return a > b;}
template <typename T> inline bool chmax(T& a, const T& b) {if (a < b) a = b; return a < b;}
/* main */
signed main(){
ll N,K;
cin >> N >> K;
vector<ll> a(N);
FOR(i,0,N)cin >> a[i];
vector<ll> b(N,0),c(N,0);
FOR(i,1,N)b[i] = max((ll)0,a[i-1])+b[i-1];
REP(i,0,N-1)c[i] = max((ll)0,a[i+1])+c[i+1];
FOR(i,1,N)a[i] += a[i-1];
ll ans = 0;
FOR(i,0,N-K+1){
chmax(ans,b[i] + max((ll)0,a[i+K-1]-(i ? a[i-1] : 0)) + c[i+K-1]);
}
cout << ans << endl;
}