#include <iostream>
#include <fstream>
using namespace std;
int i,g,n,s;
char prime[2000005];
int main()
{
    ifstream ka("ciur.in");
    ofstream ki("ciur.out");
    ka>>n;
    for(i=2;i<=n;i++)
    {
       if(prime[i]==0)
       {
           s++;
           for(g=i*i;g<=n;g=g+i)
           {
               prime[g]=1;
           }
       }
    }
    ki<<s;
}