#include <fstream>
#include <bitset>
#define ll long long
#define limita 2000001
using namespace std;
bitset<limita>isp;
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n,s=0;
    fin>>n;
    isp[1]=1;
    for (ll i=2;i*i<=n;i++)
        if (isp[i]==0)
        {
            for (ll j=i*i;j<=n;j+=i)
                isp[j]=1;
        }
    for (int i=1;i<=n;i++)
    {
        if (isp[i]==0)
            s++;
    }
    fout<<s;
    return 0;
}