from sys import stdin


def main():
    input = lambda: stdin.readline()[:-1]
    N = int(input())
    A = list(map(int, input().split()))

    a = A[:]
    ans = 0
    for _ in [0] * N:
        case1 = a[0] - a[1]
        case2 = a[-1] - a[-2]
        if case1 > case2:
            ans += case1
            a = a[2:]
        else:
            ans += case2
            a = a[:-2]
    print(ans)


main()