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


    fout<<nr;
    fout.close();
    return 0;
}