#include <fstream>
#include <cstring>

using namespace std;

int main(void)
{
   ifstream cin("ciur.in");
   ofstream cout("ciur.out");
   int n;
   cin >> n;
   char prime[2000001];
   memset(prime,1,sizeof(prime));
   prime[2]=1;
   int start=2;
   int i;
   while(start<=n)
   {
      if(prime[start]==0)
      {
       start++; 
         continue;
      }
      for(i=start*2;i<=n;i+=start)
        prime[i]=0;
      start++;               
   }
   int result =0;
   for(i=2;i<=n;i++)
      if(prime[i]==1)
        result++;
   cout << result;
   cin.close();
   cout.close();
   return 0;   
}