#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int nr=0, n, i, j,a[10005],cate;
int main()
{
bool a[2000001];
f>>n;
cate=0;
for (i=2;i<=n;i++)
  a[i]=1;
for (i=2;i<=sqrt(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]) cate++;
g<<cate;
return 0;
}