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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long int ll;
int main(){
int n, ans=0; cin>>n;
vector<bool>v(1e6, false);
while (n--){
int a; cin>>a;
if (v[a-1]==true){
v[a-1]=false;
if (a-2>=0) v[a-2]=true;
}else{
ans++;
if (a-2>=0) v[a-2]=true;
}
}cout<<ans<<endl;
return 0;
}
