fi=open("bai6.inp","r")
fo=open("bai6.out","w")
n=int(fi.readline())
a=list(map(int,fi.readline().split()))
a=[0]+a
tong=0
for i in range(2,n+1):
tong=max(tong,a[i]+a[i-1])
print(tong)
fi.close()
fo.close()