# include <iostream>
# include <fstream>
# include <bitset>
using namespace std;
# define MAXN 2000003
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset<MAXN> prim;
int main()
{
    int n, s = 0;
    fin >> n;
    prim.set();
    for (int i = 2; i <= n; i++)
    {
        if (prim[i] == true)
        {
            s++;
            for (int j = i + i; j <= n; j += i)
            {
                prim[j] = false;
            }
        }
    }
    fout << s;
}