/*#include<fstream>
long p[2000001]
using namespace std;
int main()
{
    long n, i,j,nr=0,x ;
    long max=2000000;
    for (i=2;i<=max;++i)
       if(p[i]==0)
       {
           nr++;
           for (j=i+i; j<=max;j+=i)
            p[j]=1;
       }

    ifstream f("eratostene.in");
    ofstream g("eratostene.out");
    f>>n;j=0;
    for(i=1;i<=n;i++)
       {f>>x;
        if (p[x]==0) j++;
       }
    g<<j;
    f.close();
    g.close();
    return 0;
}
*/

#include<fstream>
long p[2000001];
using namespace std;
int main()
{  ifstream f("eratostene.in");
    ofstream g("eratostene.out");
    long n, i,j,nr=0;

      f>>n;
      for (i=2;i<=n;++i)
       if(p[i]==0)
       {
           nr++;
           for (j=i+i; j<=n;j+=i)
            p[j]=1;
       }

    g<<nr;
    f.close();
    g.close();
    return 0;
}