#include<fstream.h>
#define dim 2000001
char v[dim];
long n,nr;
void ciur()
{long i,j;
for(i=2;i<=n;i++)v[i]=1;
j=1;char ok=1;
while(ok)
 {while(!v[j]&&(j<=n))j++;
  if(j<=n)
   {nr++;
    for(i=j+1;i<=n;i++)
     if(v[i])
      if(!(i%j))v[i]=0;
    j++;
   }
  else ok=0;
 }
}
int main()
{ifstream f("ciur.in");
f>>n;
f.close();
ciur();
ofstream g("ciur.out");
g<<nr<<'\n';
g.close();
return 0;
}