#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool s[2000005];
int main()
{
    int n,t=0;
    in>>n;
    for (int i=2;i<=n;i++)
    {
        if (s[i]==false)
        {
            t++;
            for (int j=i;j<=n;j=j+i)
                s[j]=true;
        }
    }
    out<<t;
    return 0;
}