#include "bits/stdc++.h" using namespace std; //#include "atcoder/all" //using namespace atcoder; #define int long long #define REP(i, n) for (int i = 0; i < (int)n; ++i) #define RREP(i, n) for (int i = (int)n - 1; i >= 0; --i) #define FOR(i, s, n) for (int i = s; i < (int)n; ++i) #define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; --i) #define ALL(a) a.begin(), a.end() #define IN(a, x, b) (a <= x && x < b) template<class T>istream&operator >>(istream&is,vector<T>&vec){for(T&x:vec)is>>x;return is;} template<class T>inline void out(T t){cout << t << "\n";} template<class T,class... Ts>inline void out(T t,Ts... ts){cout << t << " ";out(ts...);} template<class T>inline bool CHMIN(T&a,T b){if(a > b){a = b;return true;}return false;} template<class T>inline bool CHMAX(T&a,T b){if(a < b){a = b;return true;}return false;} constexpr int INF = 1e18; signed main(){ int N; cin >> N; vector<int>a(N); cin >> a; sort(ALL(a)); reverse(ALL(a)); vector<int>dp(N, INF); REP(i, N) { auto itr = lower_bound(ALL(dp), a[i] + 2); dp[itr - dp.begin()] = a[i]; } int ans = N; RREP(i, N) { if(dp[i] == INF) ans = i; } out(ans); }