import io
import sys

sys.stdin = io.StringIO('''4
2 6 4 1''')  # 7

n = int(input())
a = list(map(int, input().split()))
dp0, dp1 = 0, a[0]
for i in range(1, n):
    dp0, dp1 = dp1, max(dp1, dp0 + a[i])

print(dp1)