#include<iostream>
#include<fstream>
#include<cmath>
using namespace std;
int n,nr=1,rad;
int prim(int x){
int i;
if(x<=1)return 0;
if(x==2)return 1;
if(x%2==0)return 0;
rad=int(sqrt(x));
for(i=3;i<=rad;i+=2)
    if(x%i==0)return 0;
return 1;

}


int main(){int i,rad;
ifstream f("ciur.in");
ofstream g("ciur.out");
f>>n;
rad=int(sqrt(n));
for(i=3;i<=n;i+=2)
    if(prim(i))nr++;
    g<<nr<<"\n";



f.close();
g.close();
return 0;}