#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream fin; ofstream fout;
char p[2000000/2+1];
int n,c=1,i,j;
int f(int nr)
{
    c=1;
    for(i=1; (i<<1)+1<=nr;i+=1)
        if(p[i]==0){
            c++;
            for(j=i+i+i+1;(j<<1)+1<=nr;j+=(i<<1)+1)
                p[j]=1;
        }
    return c;
}
int main()
{
    fin.open("ciur.in"); fout.open("ciur.out");
    fin>>n;fin.close();
    cout<<f(n);
    fout<<c<<"\n";fout.close();
    return 0;
}