#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream fin; ofstream fout;
char p[1000000/2+1];
int n,c=1;
int main()
{
    fin.open("ciur.in"); fout.open("ciur.out");
    fin>>n;fin.close();

    int i,j;
    for(i=1;((i*i)<<1)+(i<<1)<=n;i++)
        if(!(p[i])){
            for(j=((i*i)<<1)+(i<<1);(j<<1)+1<=n;j+=(i<<1)+1)
                p[j]=1;
        }
    for(i=2;i<=n/2;i++)
        if(!(p[i]))c++;
    fout<<c<<"\n";fout.close();
    return 0;
}