#include <fstream>
using namespace std;

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

unsigned long long n,i,j,nr=1;
short v[1000001];

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

    g<<nr<<"\n";

    f.close();
    g.close();
    return 0;
}