import sys
input=sys.stdin.readline
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))

def main():
    mod=10**9+7
    N=I()
    A=LI()
    L=[]
    for i in range(0,2*N,2):
        a=A[i]
        b=A[i]
        L.append(a-b)
    L2=[]
    for i in range(N):
        L2.append(-1*L[i])
        
    S=[0]*(N+1)
    for i in range(N):
        S[i+1]=S[i]+L[i]
        
    S2=[0]*(N+1)
    for i in range(N-1,0,-1):
        S[i]=S[i+1]+L2[i]
        
    ans=-10**20
    for i in range(N):
        temp=S[i]+S2[i]
        if temp>ans:
            ans=temp

            
    print(ans)
    
    


main()