#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 100000 + 10;
int n,k;
int a[N],opt[N];
int sum[N],v[N];
int Pre[N],ans;
int que[N],f,r;
priority_queue < pair <int,int> > q;
int read() {
	char ch;
	int sum = 0,flag = 1;
	ch = getchar();
	while(ch < '0' || ch > '9') {
		if(ch == '-') flag = -flag;
		ch = getchar();
	}
	while(ch >= '0' && ch <= '9') {
		sum = sum * 10 + ch - '0';
		ch = getchar();
	}
	return sum * flag;
}
signed main() {
	n = read();
	k = read();
	for(int i = 1; i <= n; i++) {
		a[i] = read();
		sum[i] = sum[i - 1] + a[i];
		Pre[i] = max(1ll,i - k + 1ll);
		v[i] = sum[i] - sum[Pre[i] - 1];
	}
	f = 1,r = 0;
	for(int i = 1; i <= n; i++) {
		opt[i] = v[i];
		if(i >= k + 2) {
			q.push(make_pair(opt[Pre[i] - 2],Pre[i] - 2));
			int x = q.top().second;
			opt[i] = max(opt[i],opt[x] + v[i]);
		}
		while(que[f] < i - k && f <= r) f++;
		if(i - 2 >= 1) {
			while(opt[i - 2] - sum[i - 1] > opt[que[r]] - sum[que[r] + 1] && f <= r) r--;
			que[++r] = i - 2;
		}
		if(f <= r) opt[i] = max(opt[i],opt[que[f]] - sum[que[f] + 1] + sum[i]);
	}
	for(int i = 1; i <= n; i++) ans = max(ans,opt[i]);
	printf("%lld\n",ans);
	return 0;
}