#include <fstream>
#include <cmath>
using namespace std;
ifstream in ("ciur.in");
ofstream out("ciur.out");

int main()
 {
int a[1001];
int nr = 0, n, i, j;
in >> 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++;
out << nr << endl;
return 0;
}