#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <tuple>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <climits>

#define rep(i, n) for(int i = 0; i < n; i++)
#define per(i, n) for(int i = n - 1; i >= 0; i--)
using ll = long long;
#define vi vector<int>
#define vvi vector<vi>
#define vl vector<ll>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define mod 1000000007
using namespace std;
int main(){
  int n;
  cin >> n;
  vi a(n);
  rep(i, n) cin >> a[i];
  sort(all(a));
  int ans = 0, cnt = 0;
  for(int i = 1; i < n; i++){
    if(a[i - 1] + 1 == a[i]) cnt++;
    else{
      ans = max(ans, cnt);
      cnt = 0;
    }
  }
  ans = max(ans, cnt);
  cout << ans + 1 << "\n";
}