// numarul numerelor prime mai mici decat n
#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,k,i,j,v[2000010];
int main()
{ f>>n;
  for (i=2;i<=n;i++) v[i]=1;
  for (i=2;i<=n;i++)
  if (v[i]!=0) {
    k++;
    for (j=i+i;j<=n;j+=i)
        v[j]=0;
  }
  g<<k;
    return 0;
}