N = int(input())
I = [int(input()) for i in range(N)]

T = [[0 for _ in range(3)] for _ in range(N)]

T[0][0] = 0
T[0][1] = I[0]
T[0][2] = 0

for i in range(1, N):
    T[i][0] = max((T[i-1][0], T[i - 1][1], T[i - 1][2]))
    T[i][1] = T[i - 1][0] + I[i]
    T[i][2] = T[i - 1][1] + I[i]

print(max(T[-1]))