#include <bits/stdc++.h>
#define open ios::sync_with_stdio(false);
#define close fin.close(); fout.close(); return 0;
#define VMAX 2000001
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
vector<int> v(VMAX, 0);
int ciur(int n)
{
    int rez = 0;
    v[0] = v[1] = 1;
    for (int i = 2; i <= n; i++)
    {
        if (v[i] == 0)
        {
            for (int j = 2 * i; j <= n; j += i)
                v[j] = 1;
        }
    }
    for (int i = 1; i <= n; i++)
    {
        if (v[i] == 0)
            rez++;
    }
    return rez;
}
int main()
{
    open
    int n;
    fin >> n;
    fout << ciur(n);
    close
}