import itertools 
n=int(input())
A=list(map(int,input().split()))
ah=[]
for i in range(n):
    ah.append(A[2*i]-A[2*i+1])

ac=[0]+list(itertools.accumulate(ah))

ans=0
for i in range(n+1):
    ans=max(ans,-ac[-1]+ac[i]*2)

print(ans)