#include <iostream>
#include <fstream>
using namespace std;
long long i,j,prime,n;
bool Prim[2000001];
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
    f>>n;
    prime=1;
    for (i=2;i<=n;i+=2)
    {
        Prim[i]=true;
    }
    for (i=3;i<=n;i+=2)
    {

        if (Prim[i]==false)
        {
            prime++;
            for (j=i*i;j<=n;j=j*i)
            Prim[j]=true;
        }
    }
    g<<prime;
}