#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    bool a[2000001];
    int nr=0, n, i, j;
    f>>n;
    for (i=1;i<=n;i++)
        a[i]=1;

    for (i=2;i<=sqrt(n);i++)
    {
        for (j=i;j<=n/i;j++)
        a[i*j]=0;
    }

    for (i=2;i<=n;i++)
    if (a[i]==1) nr++;
    g<<nr;
    return 0;
}