import itertools
N = int(input())
A = list(map(int, input().split()))
AH = []
for i in range(N):
    AH.append(A[2*i]-A[2*i+1])
 
AC = [0]+list(itertools.accumulate(AH))
 
ans = 0
for i in range(N+1):
    ans = max(ans,-AC[-1]+AC[i]*2)
 
print(ans)