#include <bits/stdc++.h>
#define N 1000005
#define ll long long int
#define MP make_pair
#define pb push_back
#define ppb pop_back
#define sp " "
#define endl "\n"
#define fi first
#define se second
#define ii pair<int,int>
#define lli pair<ll,ll>
#define fast cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false)
#define fast2 freopen ("kmp.in","r",stdin);freopen ("kmp.out","w",stdout);
#define mod 1000000009
#define fs(x,y) for(int i=1;i<=y;i++) cin>>x[i]
#define fo(i,x,y) for(int i=x;i<=y;i++)
#define INF 1000000000005
using namespace std;
ll n,m,ar[N],sum,tut[N];
int main()
{
fast;
cin>>n;
fo(i,1,n)
{
int x;
cin>>x;
tut[x]++;
if(tut[x+1])
tut[x+1]--;
else
sum++;
}
cout<<sum;
}
/* cd onedrive\desktop\kod
cls
*/
