n = int(input())
a = [int(i) for i in input().split()]

rt = [0]*n
for i in range(n):
    rt[i] = a[2*n-1-(i*2)]-a[2*n-1-(i*2+1)]

rui = [0]*(n+1)
for i in range(n):
    rui[i+1] = rui[i]+rt[i]
#print(rui)
#exit()
ans = rui[n]
tmp = 0
for i in range(n):
    tmp += a[i*2]-a[i*2+1]
    ans = max(ans,tmp+rui[n-i-1])
print(ans)