#include <bits/stdc++.h>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int k;
void SieveOfEratosthenes(int num) {
   bool pno[num+1];
   memset(pno, true, sizeof(pno));
   for (int i = 2; i*i<= num; i++) {
      if (pno[i]==true) {
         for (int j = i*2; j<= num; j += i)
         pno[j] = false;
      }
   }
   for (int i = 2; i<= num; i++)
   if (pno[i])
    k++;

}
int main() {
   int num;
   fin>>num;
   SieveOfEratosthenes(num);
   fout<<k;
   return 0;
}