#include <cstdio>
using namespace std;
#define maxN 2000005
int N;
bool p[maxN];
int main ()
{
freopen ("ciur.in" , "r" , stdin);
freopen ("ciur.out" , "w" , stdout);
scanf ("%d" , &N);
for (int i = 2 ; i <= N ; ++i)
if (!p[i])
for (int j = i + i ; j <= N ; j += i)
p[j] = true;
int cont = 0;
for (int i = 2 ; i <= N ; ++i)
if (!p[i])
++cont;
printf ("%d" , cont);
return 0;
}