#include <iostream>
#include <fstream>


using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int v[2000005];
int n,cnt;
int main()

{
    f >> n;
    for ( int i = 2 ; i <= n; ++i)
        {
            if (!v[i] )
            {
                ++cnt;
                for ( int j = i+i; j <= n ; j = j + i)
                    v[j] = 1;
            }
        }
       g << cnt ;

    return 0;
}