#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];

int main()
{
    int n,i,k,f,nr=0;
    in>>n;

    for(k=2;k*k<=n;k++)
    {
        if(!v[k])
        {
            for(f=k*k;f<=n;f=f+k)
                v[f]=true;
        }
    }
    for(i=1;i<=n;i++)
        if(!v[i])
            nr++;
    out<<nr-1;
    return 0;
}