def main():
    N = int(input())
    A = [int(i) for i in input().split()]
    B = [A[i] - A[i+1] for i in range(0, 2*N, 2)]
    # print(B)
    from itertools import accumulate
    S = [a for a in accumulate([0] + B)]
    # print(S)
    ans = -(10**9)
    for i in range(N+1):
        ans = max(ans, S[i] - S[0] - (S[N] - S[i]))
    print(ans)


if __name__ == '__main__':
    main()