n = int(input())
a = list(map(int, input().split()))

lis=[]
for i in range(n):
    dif = a[2*i] - a[2*i+1]
    lis.append(dif)

l_lis=[0]
now=0
for i in range(len(lis)):
    now+=lis[i]
    l_lis.append(now)

r_lis=[0]
now=0
for i in reversed(range(len(lis))):
    now+=lis[i]
    r_lis.append(now)
r_lis.reverse()

ans=-10**20
for i in range(len(lis)):
    ans = max(ans,l_lis[i] - r_lis[i])
print(ans)