#include <fstream>
#include <math.h>
using namespace std;
 ifstream g("ciur.in")
 ofstream f("ciur.out")
int main() {
int v[1000];
int cont = 0, n, i, j;

g>> n;
for (i = 2; i <= n; i++)
v[i] = 1;
for (i = 2; i <= sqrt(n); i++)
if (v[i] != 0)
for (j = 2; j <= n / i; j++)
v[i*j] = 0;
for (i = 2; i <= n; i++)
if (v[i] != 0)
++cont;
f << cont << endl;
return 0;
}