#include <iostream>
#include <fstream>

using namespace std;

unsigned char v[2000001];
int main()
{
ifstream fin("ciur.in");
ofstream fout("ciur.out");

    int nrprime=1,n,k=0,i;
    fin>>n;
    for(i=3; i<=n; i++,i++)
    {
        if(!v[i])
        {
            nrprime++;
            for(k=i+i;k<=n;k+=i)
            {
                v[k]=1;
            }
        }
    }

    fout<<nrprime;
    return 0;
}