#include<bits/stdc++.h>

using namespace std;

ifstream f ("ciur.in");
ofstream g("ciur.out");

bool p[2000001];
int n,ans;
// p[i]=0 i e prim
//p[i]=1 i nu e prim


int main()
{
   f>>n;
   ans=0;
   p[1]=1;
   for (int i=4;i<=n;i=i+2)
     p[i]=1;
   for (int i=3;i*i<=n;i++)
    if (p[i]==0)
      {

        for (int j=i*i;j<=n;j+=2*i)
          p[j]=1;
      }
  for (int i=1;i<=n;i++)
  if (p[i]==0)
    ans++;
  g<<ans;
}