#include <fstream>

using namespace std;
ifstream cin("roci.in");
ofstream cout("roci.out");
int n,i,x,fr[10001],nr;
int main()
{
    cin>>n;
    nr=0;
    for(i=1;i<=n;i++){
        cin>>x;
        if(fr[x-1]!=0){
            fr[x]++;
            fr[x-1]--;
        }
        else{
            nr++;
            fr[x]++;
        }
    }
    cout<<nr;
    return 0;
}