import heapq
import sys
sys.setrecursionlimit(10**9)
input = sys.stdin.readline

N = int(input())
try:
    A = [int(input()) for _ in range(N)]
    cand = []
    for i in range(N):
        for j in range(i+1, N):
            heapq.heappush(cand, -A[i]-A[j])
    _ = heapq.heappop(cand)
    print(-heapq.heappop(cand))


except:
    print("assert")