// Ciur are O(n)
#include <fstream>
#include <bitset>

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

int n,p[1000000],k;
bitset <2000000> v;

int main()
{
    f>>n;
    k=1;
    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) //  inca un numar prim
        {
            ++k;
            p[k]=i;
            for (int j=2*i; j<=n; j+=i) v[j]=1;
        }
    }
    g<<k<<'\n';
    f.close();
    g.close();
    return 0;
}