#include <iostream>
#include <fstream>
#include <cmath>
#define dim 2000000
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool b[dim]={0};
int n,i,j,rn,nr=0;
int main()
{  b[0]=1;b[1]=1;
    f>>n;rn=sqrt(n);
  for(i=2;i<=rn;i++)
  {if(b[i]==0){nr++;
               for(j=i*i;j<=n;j+=i)
                  b[j]=1;
              }
  }
  for(i=rn+1;i<=n;i++)
    if(b[i]==0)nr++;
    g<<nr;

}