#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
char a[2000001];
int n,i,j,r;
int main()
{fin>>n;
 a[2]=1;
 for(i=3;i<=n;i=i+2) a[i]=1;
 for(i=3;i*i<=n;i=i+2)
    {if(a[i]==1)
     for(j=i*3;j<=n;j=j+i*2)
        a[j]=0;
    }
 for(i=2;i<=n;i++)
    if(a[i]==1)r++;
   fout<<r;
}