#include<fstream>
using namespace std;
int n,k;
char prim[2000005];
int main(void)
{int i,j;
 ifstream f("ciur.in");
 ofstream g("ciur.out");
 f>>n;
  for(i=2;i<=n;++i)
  prim[i]=1;
  for(i=2;i<=n;++i)
  if(prim[i])
   {k=k+1;
    for(j=i+i;j<=n;j=j+i)
    prim[j]=0;
}
 g<<k;
 return 0;
}