https://www.acmicpc.net/problem/2156
import sys
sys.setrecursionlimit(10**6)
input=sys.stdin.readline
n=int(input())
arr=[0]*n
for i in range(n):
arr[i]=int(input())
vals=[0]*n
def find(idx):
if idx>=n:
return 0
if vals[idx]==0:
if idx+1==n:
vals[idx]=arr[idx]
else:
vals[idx]=max(find(idx+1), arr[idx]+find(idx+2), arr[idx]+arr[idx+1]+find(idx+3))
return vals[idx]
print(find(0))
import sys
input=sys.stdin.readline
n=int(input())
arr=[0]*n
for i in range(n):
arr[i]=int(input())
vals=[0]*n
if n==1:
vals[0]=arr[0]
elif n==2:
vals[0]=arr[0]+arr[1]
else:
vals[0]=arr[0]
vals[1]=arr[0]+arr[1]
vals[2]=max(vals[1], arr[0]+arr[2], arr[1]+arr[2])
for i in range(3, n):
vals[i]=max(vals[i-1], vals[i-2]+arr[i], vals[i-3]+arr[i-1]+arr[i])
print(max(vals))