import bisect
import copy
import decimal
import fractions
import heapq
import itertools
import math
import random
import sys
import time
from collections import Counter,deque,defaultdict
from functools import lru_cache,reduce
from heapq import heappush,heappop,heapify,heappushpop,_heappop_max,_heapify_max
def _heappush_max(heap,item):
    heap.append(item)
    heapq._siftdown_max(heap, 0, len(heap)-1)
def _heappushpop_max(heap, item):
    if heap and item < heap[0]:
        item, heap[0] = heap[0], item
        heapq._siftup_max(heap, 0)
    return item
from math import gcd as GCD
read=sys.stdin.read
readline=sys.stdin.readline
readlines=sys.stdin.readlines
write=sys.stdout.write

N,K=map(int,readline().split())
A=list(map(int,readline().split()))
A1=[(A[i],-i) for i in range(1,N,2)]
_heapify_max(A1)
ans=0
min_i=N-1
queue=[]
while K:
    a,i=_heappop_max(A1)
    i=-i
    if i<min_i:
        for j in range(i+1,min_i+1,2):
            _heappush_max(queue,A[j])
        min_i=i
        ans+=a
        K-=1
    else:
        _heappush_max(queue,a)
    while K and queue and queue[0]>=a:
        ans+=queue[0]
        _heappop_max(queue)
        K-=1
print(ans)