#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
#define MAX 2000100

int i, a[MAX], n, j, s;

int main()
{
    fin >> n;
    for(i = 2 ; i <= n ; i++)
    {
        if(a[i] == 0)
        {
            s++;
            for(j = i * i ; j <= n ; j += i)
                a[j] = 1;
        }
    }
    fout << s << "\n";
}