#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000001];
void ciur()
{
    int p,i;
    for (i=2;i<=2000000;i++)
        if (v[i]==0)
        {
            p=i;
            for (i=p;i<=2000000;i+=p)
                v[i]=1;
        }
}
int main()
{
    int n,s=0,i;
    in >> n;
    ciur();
    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
            s++;
    }
    out << s;
    return 0;
}