n = int(input())
a = list(map(int,input().split()))
hom = 0
tmp = 0
for i in range(n):
    if len(a) == 2:
        if a[0] >= a[1]:
            hom += a[0]
            tmp += a[1]
            break
            
        else:
            hom += a[1]
            tmp += a[0]
            break
    else:
        if a[0] >= a[1]:
            hom += a.pop(0)
            tmp += a.pop(0)
            if len(a) == 0:
                break
        if a[-1] >= a[-2]:
            hom += a.pop()
            tmp += a.pop()
            if len(a) == 0:
                break
        if a[1] > a[0] and a[-2] > a[-1] and len(a) > 2:
            if abs(a[1] - a[0]) >= abs(a[-2] - a[-1]):
                hom += a.pop()
                tmp += a.pop()
            else:
                hom += a.pop(0)
                tmp += a.pop(0)
print(hom-tmp)