#include <fstream>
#include <cmath>
using namespace std;
bool v[2000005];
int n, k;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int main()
{
    fin >> n;
    for (int i = 2; i <= n; i++)
        v[i] = 1;
    for (int i = 2; i <= n; i++)
    {
        if (v[i] == 1)
        {
            for (int j = 2; i * j <= n; j++)
            {
                v[i * j] = 0;
            }
        }
    }
    for (int i = 2; i <= n; i++)
        {if (v[i] == 1) k++;}
    fout << k;

    return 0;
}