#include <iostream>
#include <fstream>
using namespace std;
int n,i,nrp,j;
bool v[2000001];
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in>>n;
  //prime[++nrp]=2;
  nrp++;
    for(i=3;i<=n;i=i+2)
    {
        if(v[i]==false)
            for(j=2*i;j<=n;j=j+i)
            v[j]=true;
        if(v[i]==false)
        //prime[++nrp]=i;
        nrp++;
    }
    out<<nrp;
    in.close();
    out.close();

    return 0;
}