#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <cmath>
#include <cstring>

using namespace std;

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    
    int n;
    in >> n;
    
    bool ciur[n];
    memset(ciur, true, n * sizeof(bool));
    
    for (int i = 2; i <= (int) sqrt(n); i++) {
        if (ciur[i]) {
            for (int j = 2, lim = n / i; j <= lim; j++) {
                ciur[i * j] = false;
            }
        }
    }
    
    int nr = 0;
    for (int i = 2; i < n; i++) if (ciur[i]) nr++;
    
    out << nr << "\n";
    
    in.close();
    out.close();
    return 0;
}