#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int a[10000];
int main()
{
    int n,contor,aux;
    fin>>n;
    contor=0;
    for (int i=2;i*i<=n;i++)
    {
        if (a[i]==0)
            for (int j=i+i;j<=n;j=j+i)
                a[j]=1;
    }
    for (int i=2;i<=n;i++)
        if (a[i]==0)
            contor++;
    fout<<contor;
    return 0;
}