#include <fstream>
#define LMAX 2000002

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

bool prime[LMAX];
int n;
int af;

int main()
{
    fin>>n;
    for (int i=2;i*i<=n;i++)
        if (!prime[i])
            for (int j=i*i;j<=n;j+=i)
                prime[j]=1;
    for (int i=2;i<=n;i++)
        if (!prime[i])
             af++;
    fout<<af<<'\n';
    fin.close();
    fout.close();
}