#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n,nr;
const int Nmax=2000005;
int v[Nmax];
int main()
{
    fin>>n;
    nr = 1;
    for(int i=3;i*i<=n;i+= 2)
    {
        if(!v[i])
        {
            for(int j=i*i;j<=n;j+=2*i)
            {
                v[j]=1;
            }
        }
    }
    for (int i = 3; i <= n; i += 2) {
        if (v[i] == 0) {
            nr++;
        }
    }
    fout<<nr;
    return 0;
}