N=int(input())
A=list(map(int,input().split()))
homur_count = 0
kenji_count = 0
for i in range(N):
    if max(A[0]-A[1],A[-1]-A[-2])==A[0]-A[1]:
        homur_count += A[0]
        kenji_count += A[1]        
        A=A[2:]
    else:
        homur_count+=A[-1]
        kenji_count+=A[-2]
        A=A[:-2]
    #print(A)
print(homur_count-kenji_count)