#include <fstream>
#include <bitset>
#include <cmath>
using namespace std;
int n, sol, nr;
bool v[2000005];

ifstream fin("ciur.in");
ofstream fout("ciur.out");

void mark_prim_numbers()
{
    for(int i = 2; i <= 1000000; ++i)
        if(!v[i])
          for(int j = 2; j <= 2000000 / i; ++j)
             v[i * j] = 1;
}
int main()
{
   int n, nr = 0;
   mark_prim_numbers();
   fin >> n;
   for(int i = 2; i <= n; ++i)
    if(!v[i]) nr++;
   fout << nr;
   return 0;
}