#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include <map>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <stack>
#include <algorithm>
#include <array>
#include <unordered_set>
#include <unordered_map>
#include <string>
using namespace std;

bool rcmp(int a, int b) { return a>b; }
typedef long long LL;
class mypcmp {
public:
    bool operator()(const int& a, const int& b) {
        return a<b;
    }
};


int as[200004];
LL ss[200004];
LL dp[200004];
int main() {
    int n, i, k;
    LL r;
    scanf("%d %d", &n, &k);
    dp[n]=dp[n+1]=0;
    priority_queue<pair<LL, int>> q;
    for (i=0; i<n; i++) scanf("%d", &as[i]);
    ss[0]=0; for (i=0; i<n; i++) ss[i+1]=ss[i]+as[i];
    q.push({ss[n], n+1});
    for (i=n-1; i>=0; i--) {
        r = dp[i+1];
        while(!q.empty()) {
            auto x = q.top();
            if (x.second-i<=k) break;
            q.pop();
        }
        if (!q.empty()) {
            auto x = q.top();
            r = max(r, x.first-ss[i]);
        }
        dp[i]=r;
        q.push({dp[i+1]+ss[i], i+1});
    }
    printf("%lld\n", dp[0]);
    return 0;
}