using namespace std;
#include<stdio.h>
#include<bitset>
FILE *f=fopen("ciur.in","r"),
     *g=fopen("ciur.out","w");
bitset<2000007>a;
int n,j,nr;
long long i;
int main()
{ fscanf(f,"%d",&n);
  nr=1;
  for(i=3;i*i<=n;i+=2) if(a[i]==0) { for(j=i*i;j<=n;j+=i) a[j]=1;
                                   ++nr;
                                 }
  fprintf(g,"%d\n",nr);
  fclose(f);
  fclose(g);
  return 0;
}