from collections import deque
N = int(input())
A = deque(map(int, input().split()))

a, t = 0, 0
for _ in range(N):
    if A[0] - A[1] > A[-1] - A[-2]:
        a += A[0]
        t += A[1]
        A.popleft()
        A.popleft()
    else:
        a += A[-1]
        t += A[-2]
        A.pop()
        A.pop()

print(a - t)