#include <fstream>

using namespace std;

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

bool c[2000001];

int main()
{   int n, i, ct = 0, j;
    fin >> n;
    fin.close();
    c[2] = 1;
    for ( i = 3; i <= n; i = i + 2 )
         c[i] = 1;
    for ( i = 3; i * i <= n; i++ )
         if ( c[i] == 1 )
             for ( j = 3 * i; j <= n; j = j + 2 * i )
                  c[j] = false;
    for ( i = 1; i <= n; i++ )
         if ( c[i] == 1 ) ct++;
    fout << ct;
    fout.close();
    return 0;
}