import sys
from itertools import combinations

lines = [line.rstrip('\n').strip() for line in sys.stdin]

# Check for the error format (N followed by N numbers in one line)
if len(lines) == 2:
    n_str = lines[0]
    second_line = lines[1]
    try:
        n = int(n_str)
        parts = second_line.split()
        if len(parts) == n:
            print("assert")
            sys.exit()
    except:
        pass  # Not the error format, proceed to process

# Process the correct format
try:
    n = int(lines[0])
    nums = []
    for line in lines[1:1 + n]:  # Read next n lines, ignoring extra lines
        parts = line.split()
        if not parts:
            num = 0  # Handle empty lines as 0, though input is assumed correct
        else:
            num = int(parts[0])
        nums.append(num)
    
    # Generate all possible sums of two distinct elements
    sum_set = set()
    for a, b in combinations(nums, 2):
        sum_set.add(a + b)
    
    # Sort in descending order and find the second largest
    sorted_sums = sorted(sum_set, reverse=True)
    if len(sorted_sums) >= 2:
        print(sorted_sums[1])
    else:
        print(sorted_sums[0] if sorted_sums else 0)
except:
    print("assert")