#include <fstream>
#include<cmath>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool a[2000001];
int main()
{
 int  n, i, j,gigel=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] == 1)
    gigel++;

out<<gigel;

return 0;
}