import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())

n=I()
v=LI()
dp=[[-1 for _ in range(2)] for _ in range(n+1)]

dp[0][0]=0

for i in range(n):
  dp[i+1][0]=max(dp[i+1][0],dp[i][0],dp[i][1])
  dp[i+1][1]=max(dp[i+1][1],dp[i][0]+v[i])

print(max(dp[n][0],dp[n][1]))