#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <set>
#include <map>
using namespace std;

int countItems(multiset<int> a, int x) {
    int count = 0;
    for(multiset<int>::iterator it = a.find(x); it != a.end() && *it == x; ++it)
        count++;
    return count;
}

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n, temp;
    cin >> n;
    multiset<int> a;
    for(int i = 0; i < n; i++) {
        cin >> temp;
        a.insert(temp);
    }
    
    map<pair<int, int>, int> sols;
    
    pair<int, int> bestPair;
    int maxCount = 0;
    
    int e;
    map<pair<int, int>, int>::iterator itSol;
    pair<int, int> solPair;
    
    for(int i : a) {
        e = 1;
        solPair = pair<int, int>(i, i + e);
        itSol = sols.find(solPair);
        if(itSol != sols.end()) {
            if(itSol->second > maxCount) {
                maxCount = itSol->second;
                bestPair = solPair;
            }
        }
        else {
            int count = countItems(a, i) + countItems(a, i + e);
            sols.emplace(solPair, count);
            if(count > maxCount) {
                maxCount = count;
                bestPair = solPair;
            }
        }
        e = -1;
        solPair = pair<int, int>(i, i + e);
        itSol = sols.find(solPair);
        if(itSol != sols.end()) {
            if(itSol->second > maxCount) {
                maxCount = itSol->second;
                bestPair = solPair;
            }
        }
        else {
            int count = countItems(a, i) + countItems(a, i + e);
            sols.emplace(solPair, count);
            if(count > maxCount) {
                maxCount = count;
                bestPair = solPair;
            }
        }
    }
    
    cout << maxCount << endl;
    
    
    
    return 0;
}