#include <iostream>
#include <fstream>
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

char v[2000005];
int main()
{
    int n;
    in >> n;
    int rez = 0;
    for(int i = 2;i <= n;i++)
        v[i] = 1;
    for(int i = 2;i <= n;i++)
        if(poz[i])
        {
            rez++;
            for(int j = i;j <= n;j+=i)
                poz[j] = 0;
        }
        out << rez;
    return 0;
}