n = int(input())
*a, = map(int,input().split())
res = [0]*(n+1)
for i in range(n):
    res[i] = a[2*i]-a[2*i+1]
t = sum(res)
for i in range(n)[::-1]:
    res[i] += res[i+1]
ans = -1<<31
for i in range(n+1):
    ans = max(ans,t-2*res[i])
print(ans)