#include <iostream>
#include <fstream>
using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int p[2000001];
int main()
{
    int n,nr=0;
    fin>>n;
    for (int i=2;i<=n;i++) p[i]=1;
    for (int i=2;i<=n;i++)
        if (p[i]!=0)
        {
            nr++;
            for (int j=i;j<=n;j+=i) p[j]=0;
        }
    fout<<nr;

    return 0;
}