N = int(input())
A = [int(a) for a in input().split()]

h = 0
t = 0
for i in range(2*N):
    if i%2 == 0:
        h += A[i]
    else:
        t += A[i]

ans = h-t
for i in range(2*N-1, -1, -2):
    h += A[i]-A[i-1]
    t -= A[i]-A[i-1]
    ans = max(ans, h-t)

print(ans)