#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main() {
	int n;
	cin >> n;
	vector<int> a(n);
	vector<int> count;
	count.assign(100, 0);

	for (int a_i = 0; a_i < n; a_i++) {
		cin >> a[a_i];
		++count[a[a_i]];
	}
	int max = 0;
	for (int minIdx = 0, maxIdx = 1; maxIdx < 100; ) {
		int actSum = count[minIdx] + count[maxIdx];
		if (actSum > max) {
			max = actSum;
		}
		++minIdx;
		++maxIdx;
	}
	cout << max << endl;
	return 0;
}