# include <iostream>
# include <fstream>
# include <bitset>

using namespace std;

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

int n, s;
bitset <2000005> E;

int main ()

{
        fin >> n;
        E[0] = 1;
        E[1] = 1;
        for ( int i = 2; i <= n; ++i)
            if (E[i] == 0) {
                ++s;
                for ( int j = i + i; j <= n; j += i)
                E[j] = 1;
            }
        fout << s;
return 0;
}