#include <iostream>
#include <fstream>
#include <bitset>
#define NMAX 2000005
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
bitset<NMAX> v;
int n;
int main()
{
    f>>n;
    int nr = 1;
    for (int i = 3; i <= n; i+=2)
        if (v[i] == false)
        {
            nr++;
            for (int j = 2 * i; j <= n; j += i)
                v[j] = true;
        }
    g<<nr;
    return 0;
}