#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
    int a[2000002];
    int nr = 0, n, i, j;

    fin >> n;
    for (i = 2; i <= n; i++)
    {
        a[i] = 1;
    }
    for (i = 2; i * i <= n; i++)
    {
        if (a[i] != 0)
        {
            for (j = 2; j <= n / i; j++)
            {
                a[i*j] = 0;
            }
        }
    }
    for (i = 2; i <= n; i++)
    {
        if (a[i] != 0)
        {
            nr++;
        }
    }
    fout << nr << '\n';
    return 0;
}