#include <fstream>

using namespace std;

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

int c[2000001],i,j,n,nr;
int main()
{
    fin>>n;
    c[0]=1;
    c[1]=1;
    for (i=2;i*i<=n;i++)
        if (c[i]==0)
            for (j=2;j<=n/i;j++)
                c[j*i]=1;
    for (i=1;i<=n;i++)
        if (c[i]==0)
            nr++;
    fout<<nr;
    return 0;
}