#include<stdio.h>
#define N 2000001
char c[N];
long long n;
void ciur()
{
  int d=2;
  while (d*d<=n)
  {
     if (!c[d])
        for (int i=d*d; i<=n; i+=d)
             c[i]=1;++d;
  }
  long long num=0;
  for (int i=2; i<=n; ++i) if (!c[i]) ++num;
  printf("%lld",num);
}
void citire()
{
  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);
  scanf("%lld",&n);

}
int main()
{
  citire();
  ciur();
  return 0;
}