#include<fstream>
#include<math.h>
using namespace std;
bool a[2000001];
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int main()
{
    int n,i,j,m=0;
    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) m++;
out<<m;
}