#include <fstream>
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");
char v[2000000];
int main()
{
    long int n,s=0;
    in>>n;
    for(int k=2;k<=n;k++)
    {
        if(!v[k])
        {
        s++;
        for(int i=k*2;i<=n;i=k+i)
        v[i]=1;
        }
    }
    out<<s;
}