#include <iostream> #include <string> #include <vector> #include <algorithm> #include <functional> #include <cmath> #include <iomanip> #include <stack> #include <queue> #include <numeric> #include <map> #include <unordered_map> #include <set> #include <fstream> #include <chrono> #include <random> #include <bitset> //#include <atcoder/all> #define rep(i,n) for(int i=0;i<(n);i++) #define all(x) x.begin(), x.end() #define rall(x) x.rbegin(), x.rend() #define sz(x) ((int)(x).size()) #define pb push_back using ll = long long; using namespace std; template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; } template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; } ll gcd(ll a, ll b) {return b?gcd(b,a%b):a;} ll lcm(ll a, ll b) {return a/gcd(a,b)*b;} int main(){ int N; cin >> N; multiset<ll> ms; rep(i,N){ int x; cin >> x; ms.insert(x); } int ans = 0; while(!ms.empty()){ int now = -1; while(ms.lower_bound(now+2)!=ms.end()){ now = *ms.lower_bound(now+2); ms.erase(ms.find(now)); } ans++; } cout << ans << endl; return 0; }