#include <fstream>
using namespace std;
bool v[2000001];
int n, nr=0;
int main()
{
    int i , j;
    ifstream f1 ("ciur.in");
    ofstream f2 ("ciur.out");
    f1>>n;
    for (i = 2; i <= n; ++i)
        v[i] = 1;
    for (i = 2; i <= n; ++i)
        if (v[i])
        {
            nr++;
            for (j = i+i; j <= n; j += i)
                v[j] = 0;
        }
    f2<<nr;
    f1.close();
    f2.close();
    return 0;
}