#include<iostream>
#include<fstream>
using namespace std;

long n,i,j,s;
bool V[20000000];

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

int main()
{
    in>>n;
    for ( i=2; i<=n; ++i )
        if ( V[i]==0 )
        {
            s++;
            for ( j=i*2; j<=n; j+=i )
                V[j]=1;
        }
    out<<s<<"\n";
    return 0;
}