#include <iostream>
#include <fstream>
using namespace std;
fstream f("ciur.in");
ofstream g("ciur.out");
int i,n,j,nr;
int main()
{
f>>n;
int a[n*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;
}