#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;}