N = int(input())
A = list(map(int,input().split()))
D = [0]*N
for k in range(N):
    D[k] = A[2*k]-A[2*k+1]
S = [0]*N
T = [0]*N
S[0] = D[0]
T[-1] = -D[-1]
for k in range(1,N):
    S[k] = S[k-1] + D[k]
    T[-k-1] = T[-k] - D[-k-1]
ans = max(S[-1],T[0])
for k in range(N-1):
    ans = max(ans,S[k]+T[k+1])
print(ans)