if __name__ == '__main__':
    n=int(input())
    A=[int(i) for i in input().split()]
    ans=0
    while 1:
        if len(A)==1:
            hom+=A[0]
            break
        if len(A)==0:
            break
        if A[0]>A[-1]:
            ans+=A[0]-A[1]
            del A[0:2]
        else:
            ans+=A[-1]-A[-2]
            del A[-2:]

    print(ans)