#include <fstream>
using namespace std;

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

int c[2000001];

int main()
{
    int i, n, nrp = 0;
    fin >> n;
    for ( i = 2; i * i <= n; i++ )
        if ( c[i] == 0 )
            for ( int j = i + i; j <= n; j += i )
                c[j] = 1;
    for ( i = 2; i <= n; i++ )
        if ( !c[i] )
            nrp++;
    fout << nrp << '\n';
    fin.close();
    fout.close();
    return 0;
}