#include <fstream>
using namespace std;
const int Nmax = 2000000;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int k=1,i,j,n;
bool ciur[Nmax];
int main()
{
    fin>>n;
    if (n==2)
    {
        fout<<"1\n";
        return 0;
    }
    for (i = 2; i <= n; ++i) ciur[i] = 1;
    for (i = 2; i * i <= n; ++i)
        if (ciur[i])
            for (j = i * i; j <= n; j += i)
                ciur[j] = 0;
    for (i=3;i<=n;i+=2) {
        if (ciur[i]) k++;
    }
   fout << k << "\n";
    return 0;
}