n = int(input())
m = input().split()
v = [0]
sum = []
for num in range(n):
    v.append(int(m[num]))

take = [0]
nottake = [0]

for i in range(1,n+1):
    take.append(nottake[i-1]+v[i])
    nottake.append(max(take[i-1],nottake[i-1]))

print(max(nottake[n],take[n]))