#include <fstream>
#include <bitset>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

const int VMAX = 2e6;
bitset<VMAX+1> p;

int ciuruletz_smecher(int n)
{
    int ctr = 0;

    for (int i = 2; i<=n; i++)
    {
        if(!p[i]){
        ctr++;
        if(1LL*i*i<=n)
            for (int j = i*i; j<=n; j+=i)
            {
                p[j] = 1;
            }
        }
    }
    return ctr;

}
int main(){

int n;
fin>>n;
fout<<ciuruletz_smecher(n);
}