#include <fstream>
#include <bitset>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

bitset <20000001> p;
int n;

void Eratostene(){
    p[0] = p[1] = 1;
    for(int i = 2; i <= 1415; ++i)
       if(p[i] == 0)
        for(int j = 2; i * j <= 2000000; ++j)
           p[i * j] = 1;

}


int main(){

   cin >> n;
   Eratostene();

   int cnt = 0;
   for(int i = 1; i <= n; ++i)
       if(!p[i])
          cnt++;

   cout << cnt;

   return 0;
}