문제: https://www.acmicpc.net/problem/2579
문제 해결 방법
'''
패턴 확인
1 2 3 4
O X O O => d[i] = stairs[i] + stairs[i - 1] + dp[i-3]
O O X O => d[i] = stairs[i] + dp[i-2]
'''
import sys
input = sys.stdin.readline
N = int(input())
stairs = []
for n in range(N):
stairs.append(int(input()))
dp = [0] * N
if N == 1:
dp[0] = stairs[0]
if N == 2:
dp[0] = stairs[0]
dp[1] = stairs[0] + stairs[1]
if N >= 3:
dp[0] = stairs[0]
dp[1] = stairs[0] + stairs[1]
dp[2] = max(stairs[2] + stairs[1], stairs[2] + stairs[0])
for i in range(3, N):
dp[i] = max(stairs[i] + stairs[i - 1] + dp[i-3], stairs[i] + dp[i-2])
print(dp[-1])