#include <fstream>
 
using namespace std;
 
ifstream f("ciur.in");
ofstream g("ciur.out");
 
bool c[2000001];
int n, i, j, nr;
 
int main ()
{
    f >> n;
    for (i=2; i<=n; i++)
    {
        if (c[i] == 0)
        {
            nr++;
            for (j=i*2; j<=n; j=j+i)
                c[j] = 1;
        }
    }
    g << nr;
    return 0;
}