#include <fstream>
#include <iostream>

char v[2000000];

using namespace std;
ifstream in ( "ciur.in" );
ofstream out ( "ciur.out" );

int main()
{
    int i, j, n, nr;

    in>>n;

    for ( i = 2; i * i <= n; i++ ) {
        if ( !v[i] ) {
            for ( j = i * i; j <= n; j = j + i ) {
                v[j] = 1;
            }
        }
    }
    nr = 0;
    for ( i = 2; i <= n; i++ ) {
        if ( v[i] == 0 )
            nr++;
    }
    out<<nr;


    return 0;
}