#include <fstream>

using namespace std;

int n,c;

char v[2000005];

int main()
{
    int i,j;
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in >> n;
    for (i = 2; i<=n; i++)
        v[i] = 1;
    for (i = 2; i<=n; i++)
        if (v[i])
        {
            c++;
            for (j = i+i; j<=n; j+=i)
                v[j] = 0;
        }
    out << c;
}