#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int N,i,cont,j,v[2000000];
int main()
{
    f >> N;
    for(i=2;i<=N;i++)
    {
        if(!v[i])
        {
            cont++;
            for(j=2;j*i<=N;j++)
                v[i*j]=1;
        }

    }

    g<<cont;
    return 0;
}