#include <iostream>
#include <fstream>
using namespace std;
int main () {
ifstream in("ciur.in");
ofstream out("ciur.out");
long long a,b,N,i,contor=0;
in>>N;
for (a=2;a<N;a++)
{
    bool estePrim = true;
for (b=2;b<=a/2;b++)
    {
        if ( a % b == 0 )
        { estePrim = false;
        break;
        }

    }
        if( estePrim == true)
            contor++;

    }

out<<contor;
return 0;
}