N = int(input())
V = list(map(int, input().split()))
inf = 10 ** 18
dp0 = [-inf] * (N + 1)
dp1 = [-inf] * (N + 1)
dp0[0] = 0
for i in range(N):
    dp0[i + 1] = max(dp0[i + 1], dp0[i], dp1[i])
    dp1[i + 1] = max(dp1[i + 1], dp0[i] + V[i])
print(max(dp0[-1], dp1[-1]))