#include <fstream>
#include <iomanip>
using namespace std;

bool ok[2000000];
int main()
{
    
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int i, j, n, x = 0;
    fin >> n;
    for ( int i = 0; i < n; i++ )
        ok[i] = true;
    for ( i = 2; i*i <= n; i++ )
        if ( ok[i] )
        {
                j = 2;
                while ( i*j <= n )
                {
                    ok[i*j] = false;
                    j++;
                }    
        }
        for ( i = 2; i <= n; i++ )
                if ( ok[i] )
                    x++;
                        fout << x;
    fin.close();
    fout.close();
    
    return 0;
}