#include <fstream>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

int n;
bool erath[2000005];
int main()
{
    fin >> n;
    for (int div = 2; div*div <= n; div++)
    {
        if (erath[div] != 0)
            continue;
        for (int mul = 2*div; mul <= n; mul += div)
        {
            erath[mul] = 1;
        }
    }
    int cnt = 0;
    for (int i = 1; i <= n; i++)
    {
        if (erath[i] != 1)
            cnt++;
    }
    fout << cnt - 1;
    return 0;
}