#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{long long c=0,ciur[2000000], n, i, j;
fin>>n;
//initial toate numerele sunt in ciur
for (i=2; i<n; i++) ciur[i]=1;
for (i=2; i<=sqrt(n); i++)
if (ciur[i])//i este prim
//elimin toti multiplii lui i
for (j=2; j*i<n; j++)
ciur[i*j]=0;
for (i=2; i<n; i++)
if (ciur[i]) c++;
fout<<c;
return 0; }