#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
#define file freopen("in.txt", "r", stdin);
#define pii pair<int,int>
#define pb push_back
#define all(v) v.begin(), v.end()
#define keepunique(v) (v).erase(unique(all(v)),v.end())
#define fastread ios_base::sync_with_stdio(false);cin.tie(NULL);
const int maxn = 1e6 + 5;
int arr[maxn];
int freq[maxn], n;
int solve(){
int ans = 0, i = 0, t = n;
while(t > 0 and i < n){
if(freq[arr[i]] > 0){
int cnt = 0;
while(freq[arr[i]-cnt] > 0){
freq[arr[i]-cnt]--;
if(freq[arr[i]-cnt] <= 0)--t;
++cnt;
}
++ans;
}
++i;
}
return ans;
}
int main(){
//file
fastread
cin>>n;
for(int i=0; i<n; i++){
cin>>arr[i];
freq[arr[i]]++;
}
cout<<solve()<<endl;
}
