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

const int VMAX = 2000001;

using namespace std;

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

int main()
{
    bitset <VMAX> c;
    int n;
    fin >> n;
    c[0] = c[1] = 1;
    for ( int i = 2; i * i <= n; i++ )
        if ( !c[i] )
            for ( int j = i * i; j <= n; j += i )
                c[j] = 1;
    int p = 0;
    for ( int i = 2; i <= n; i++ )
        if ( c[i] == 0 )
            p++;
    fout << p;
    return 0;
}