#include <iostream>
#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool verif[2000005];

int main()
{
    int a,nr=0;
    in>>a;
    for(int i=2;i<=a;i++)
        if(!verif[i])
        {
            nr++;
            for(int j=2;i*j<=a;j++)
                verif[i*j]=1;
        }
    out<<nr;
    return 0;
}