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