import sys
from collections import defaultdict

def main():
    n = int(sys.stdin.readline())
    a = list(map(int, sys.stdin.readline().split()))
    
    # Calculate maximum frequency of any number
    freq = defaultdict(int)
    for num in a:
        freq[num] += 1
    max_freq = max(freq.values()) if freq else 0
    
    # Calculate maximum non-adjacent count using dynamic programming
    if n == 0:
        max_non_adjacent = 0
    else:
        prev_no = 0  # previous state: not taking the previous element
        prev_yes = 1  # previous state: taking the previous element
        for i in range(1, n):
            current_no = max(prev_no, prev_yes)
            current_yes = prev_no + 1
            prev_no, prev_yes = current_no, current_yes
        max_non_adjacent = max(prev_no, prev_yes)
    
    # The answer is the maximum of the two values
    print(max(max_freq, max_non_adjacent))

if __name__ == "__main__":
    main()