#include <fstream>
using namespace std;
int v[2000005];
int main()
{
    int n=0,i,t=0,k;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for (i=2;i*i<=n;i++)
        if (v[i]==0)
        {
            k=2;
            t++;
            while (i*k<=n)
            {
                v[i*k]=1;
                k++;
            }
        }
    fout<<t;
    return 0;
}