#include <bits/stdc++.h>

using namespace std;
ifstream f("8=======D.in");
ofstream g("8=======D.out");
const int NMax = 2e6 + 5;
int k;
int Prim[NMax];
bool viz[NMax];

void Ciur(int n)
{
   for(int i = 2; i <= n; i++)
        {
         if(viz[i] == 0)
         {
          k++;
          Prim[k] = i;
          for(int j = 2*i; j <= n; j = j + i)
             {
              viz[j] = 1;
             }
         }
        }
}

int main()
{
   int n;
   f >> n;
   Ciur(n);
   g << k;

    return 0;
}