#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
    int n,i=3,contor=1,d,prim;
    f>>n;
    while(i<=n)
    {
        prim=1;
        for(d=3;d<=sqrt(i);d++)
            if(i%d==0)
            {
                prim=0;
                break;
            }
        if(prim==1)
            contor++;
        i=i+2;
    }
    g<<contor;
    return 0;
}