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

int main()
{ifstream f("ciur.in");
ofstream g("ciur.out");
    int N,v[100000],i,j,cont;
    f>>N;
    for (i=2;i<N;i++)
        v[i]=1;
    cont=0;
    for (i=2;i<N;i++)
        {if (v[i])
        cont++;
        for (j=i*2;j<N;j=j+i)
            v[j]=0;}
        g<<cont;
    return 0;
}