#include <iostream>
#include <cmath>
#include <climits>
#define ll long long

using namespace std;
int main() {
	int n,k; cin>>n>>k;
	int* arr = new int[n+1]();
	for(int i =1; i<=n; ++i) cin>>arr[i];
	ll* f = new ll[n+1]();
	ll* b = new ll[n+1]();
	
	if(k+1 <=n && k+2 <= n) { 	f[k+1] = arr[k+1]; f[k+2] = arr[k+2];   }
	else if(k+1 <= n ) f[k+1] = arr[k+1];
	
	for(int i = k+ 3; i<=n; ++i) 
	f[i] = max(f[i-1],f[i-2]) + arr[i];
	
	b[1] = arr[1]; b[2] = arr[1] + arr[2];
	for(int i = 3; i <= n; ++i) 
	  b[i] = max(b[i-1],b[i-2]) + arr[i];
	
	ll ans = INT_MIN;
	for(int i =k; i<=n ;++i) 
	ans = max(ans, f[i] + b[i] - arr[i]);
	
	cout<<ans;
	
}