#include<fstream>
using namespace std;
int v[2000000],n,counter;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for(int i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
           // cout<<i<<" ";
            counter++;
            for(int j=i+i;j<=n;j=j+i)
            {
                v[j]=1;
            }
        }
    }
    fout<<counter;
}