n=int(input())
a=list(map(int,input().split()))
b=[a[i]-a[i+1] for i in range(0,2*n,2)]
c=[-i for i in b]
b=[0]+b
c+=[0]
for i in range(1,n+1):
    b[i]+=b[i-1]
for i in range(n-1,-1,-1):
    c[i]+=c[i+1]
ans=-10**18
for i in range(n+1):
    ans=max(ans,b[i]+c[i])
print(ans)