#include <iostream>
#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n, s;
bool v[2000001];

int main()
{
    f >> n;
    for ( int i = 2; i <= n; i++)
        v[i]= 1;
    for ( int i = 2; i * i<= n; i += 1)
        if ( v[i] == 1 )
        {   for ( int j = 2; j * i <= n; j += 1 )
                v[i*j] = 0;
        }
    for ( int i = 2; i <= n; i++)
        if( v[i] == 1)
            s++;
    g << s;
    f.close();
    g.close();
    return 0;
}