#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
template<class T> bool chmax(T &a, const T &b){if(a<b){a=b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b){if(a>b){a=b; return true;} return false;}
template<class T> T div_floor(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>=0 ? a/b : (a+1)/b-1;
}
template<class T> T div_ceil(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>0 ? (a-1)/b+1 : a/b;
}

constexpr lint mod = 1e9+7;
constexpr lint INF = mod * mod;
constexpr int MAX = 100010;

template<typename T> struct SegTree{
    using F=function<T(T, T)>;
    int sz=1, seq_sz;
    T et;
    F f, g;
    vector<T> node;

    SegTree(int sz_, T et_, F f_, F g_): seq_sz(sz_), et(et_), f(f_), g(g_){
        while(sz<sz_) sz<<=1;
        node.resize(sz<<1, et);
    }

    void build(vector<T> &a){
        rep(i, a.size()) node[i+sz] = a[i];
        rFor(i, sz, 1) node[i] = f(node[i<<1], node[(i<<1)+1]);
    }

    void build(T x){
        rep(i, seq_sz) node[i+sz] = x;
        rFor(i, sz, 1) node[i] = f(node[i<<1], node[(i<<1)+1]);
    }

    void update(int i, T x){
        i+=sz;
        node[i]=g(node[i], x);
        i>>=1;
        while(i){
            node[i]=f(node[i<<1], node[(i<<1)+1]);
            i>>=1;
        }
    }

    T query(int l, int r){
        T vl=et, vr=et;
        for(l+=sz, r+=sz; l<r; l>>=1, r>>=1){
            if(l&1) vl=f(vl, node[l++]);
            if(r&1) vr=f(node[--r], vr);
        }
        return f(vl, vr);
    }

    int search_left(int l, const T val, function<bool(T, T)> cmp, function<bool(T, T)> check){
        T sum = et;
        for(l+=sz; ; l>>=1){
            if(check(f(sum, node[l]), val)){
                while(l < sz){
                    if(check(f(sum, node[l<<1]), val)) l<<=1;
                    else{
                        sum = f(sum, node[l<<1]);
                        l = (l<<1) + 1;
                    }
                }
                return l-sz;
            }
            if(__builtin_popcount(l+1) == 1) return seq_sz;
            if(l&1) sum = f(sum, node[l++]);
        }
    }

    int search_right(int r, const T val, function<bool(T, T)> cmp, function<bool(T, T)> check){
        T sum = et;
        for(r+=sz; ; r>>=1){
            if(check(f(sum, node[r]), val)){
                while(r < sz){
                    if(check(f(node[(r<<1)+1], sum), val)) r = (r<<1) + 1;
                    else{
                        sum = f(node[(r<<1)+1], sum);
                        r<<=1;
                    }
                }
                return r-sz;
            }
            if(__builtin_popcount(r) == 1) return -1;
            if(!(r&1)) sum = f(node[r--], sum);
        }
    }

    int lower_bound_left(int l, const T val, function<bool(T, T)> cmp=less<>()){
        auto check = [&cmp](auto a, auto b){return !cmp(a, b);};
        return search_left(l, val, cmp, check);
    }

    int upper_bound_left(int l, const T val, function<bool(T, T)> cmp=less<>()){
        auto check = [&cmp](auto a, auto b){return cmp(b, a);};
        return search_left(l, val, cmp, check);
    }

    int lower_bound_right(int l, const T val, function<bool(T, T)> cmp=greater<>()){
        auto check = [&cmp](auto a, auto b){return !cmp(b, a);};
        return search_right(l, val, cmp, check);
    }

    int upper_bound_right(int l, const T val, function<bool(T, T)> cmp=greater<>()){
        auto check = [&cmp](auto a, auto b){return cmp(a, b);};
        return search_right(l, val, cmp, check);
    }
};

int main(){
    int n, K;
    scanf("%d%d", &n, &K);
    lint a[n];
    rep(i, n) scanf("%lld", &a[i]);
    lint sum[n+1], sum_plus[n+1];
    sum[0] = sum_plus[0] = 0;
    rep(i, n){
        sum[i+1] = sum[i] + a[i];
        sum_plus[i+1] = sum_plus[i] + max(a[i], 0LL);
    }

    lint ans = 0;
    for(int i=0; i+K<=n; ++i){
        chmax(ans, sum_plus[i] + max(0LL, sum[i+K]-sum[i]) + sum_plus[n]-sum_plus[i+K]);
    }
    printf("%lld\n", ans);
}

Measured memory_bytes: 6064