#include<cstdio>
using namespace std;
int main()
{
  long long unsigned n,i,j;
  unsigned cnt;
  char v[2000005];
  FILE *f1,*f2;
  f1=fopen("ciur.in","r");
  f2=fopen("ciur.out","w");
  fscanf(f1,"%llu",&n);
  fclose(f1);
  for(i=3;i<=n;i+=2)
    v[i]=1;
    cnt=1;
  for(i=3;i<=n;i+=2){
  if(v[i]){
      cnt++;
  for(j=i*i;j<=n;j=j+i)
    v[j]=0;
  }
  }
  fprintf(f2,"%u\n",cnt);
  fclose(f2);
  return 0;
}