#include <iostream>
#include <fstream>
#include <vector>
#include <math.h>
using namespace std;
ifstream fin; ofstream fout;
vector<int> a;
int n,c=0;
int main()
{
    fin.open("ciur.in"); fout.open("ciur.out");
    fin>>n;fin.close();
    a=vector<int>(n,1);
    int i,j;
    for(i=3;i<=n;i+=2)
        if(a[i])
        {
            c++;
            for(j=i+i;j<=n;j+=i<<1)
                a[j]=0;
        }
    fout<<c;fout.close();
    return 0;
}