N = int(input())
A = []
for _ in range(N):
    a = input()
    if a.find(" ")>=0:
        print('"assert"')
        exit()
    A.append(int(a))
B = set()
for i in range(N):
    for j in range(i+1, N):
        B.add(A[i]+A[j])
B = list(B)
B.sort(reverse=True)
print(B[1])