#include <fstream>
#include <bitset>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <2000100> a;
int n,cnt;
int main()
{
    fin>>n;
    for (int i=2;i<=n;i++)
    {
        if (a[i]==0)
        {
            cnt++;
            for (int j=2*i;j<=n;j=j+i)
                a[j]=1;
        }
    }
    fout<<cnt;
}