#include <fstream>
#include <bitset>
#define Nmax 10000000

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int n,p[2000000100],k;
bitset <Nmax> v;

int main()
{
    f>>n;
    ++k; p[k]=2;
    for (int i=4; i<=n; i+=2) v[i]=1;
    for (int i=3; i<=n; i+=2)
        if (v[i]==0)
        {
            ++k; p[k]=i;
            for (int j=2*i; j<=n; j+=i) v[j]=1;

        }
    //for (int i=1; i<=k; ++i) g<<p[i]<<' ';
    g<<k<<'\n';
    f.close(); g.close();
    return 0;
}