#include <iostream>
#include <fstream>
#include <cstdio>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int nr,a[2000001],i,j,N;
int main()
{
    f>>N;
    for(i=2;i<=N;i++)
        a[i]=1;
    for (i=2;i*i<=N;i++)
        if (a[i]) for (j=i;j<=N/i;j++)
                       a[i*j]=0;
    for (i=2;i<=N;i++)
       if (a[i]) nr++;
    g<<nr;
    return 0;
}