#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
short int p[2000002];

int main()
{
    int n, contor=0;
    fin>>n;
    for (int i=2; i<=n; i++)
    {
        if(p[i]==0)
        {
            contor++;
            for (int j=2*i; j<=n; j=j+i)
            {
                p[j]=1;
            }
        }
    }
    fout<<contor;
    return 0;
}