#include<stdio.h>
#define Nmax 2000001

FILE *fin=freopen("ciur.in","r",stdin),
     *fout=freopen("ciur.out","w",stdout);
     
int n;
long sol[1024];
char viz[Nmax];
     

void solve()
{
  int cont=0;
  for(long i=2;i<=n;i++)
    if(viz[i]==0)
    {
     for(long j=i+i;j<=n;j+=i)
       viz[j]=1;
      cont++;
    }
  printf("%d\n",cont);

}
     
int main()
{
  scanf("%d",&n);
  solve();
  printf("\n");
  return 0;
}