#include <iostream>
#include <math.h>
#include <fstream>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
long long a[200000],n;
int nr=0,i,j;
f>>n;
for (i=2;i<=n;i++)
a[i]=1;
for (i=2;i<=sqrt(n);i++)
if (a[i]!=0)
for (j=2;j<= n/i;j++)
a[i*j]=0;
for (i=2;i<=n;i++)
if (a[i]!=0)
nr++;
g<<nr<<'\n';
return 0;
}