#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
long n,ct,i,a[2000002],j;
int main()
{
    f >> n;
    ct=0;
    for (i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
            for (j=i*i;j<=n;j=j+i)
                a[j]=1;

        }
    }

    for (i=2;i<=n;i++)
        if(a[i]==0)ct++;
    g << ct;
    return 0;
}