#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000
#define int long long

signed main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int N, K;
	cin >> N >> K;
	int a[N];
	rep(i, N) cin >> a[i];
	int ans = 0;
	int tmp = 0;
	rep(i, N - K) tmp += max(0, a[i]);
	int left = 0;
	rep(i, K) left += a[N - K + i];
	ans = max(ans, tmp + max(0, left));
	rep(i, N - K) {
		//cout << tmp << " " << left << " " << ans << endl;
		//cout << N - K - i - 1 << " " << N - i - 1 << endl;
		left = left + a[N - K - i - 1] - a[N - i - 1];
		tmp = tmp - max(0, a[N - K - i - 1]) + max(0, a[N - i - 1]);
		ans = max(ans, tmp + max(0, left));
	}
	cout << ans << endl;



    return 0;
}
