#include <fstream.h>
ifstream  f("ciur.in");
ofstream g("ciur.out");
long i,n,j,l,k=1;
int v[200];
int main ()
{f>>n;
for (j=3; j<=n; j+=2)
if (v[j]==0)
{for (l=j*j; l<=n; l+=j)
v[l]=1;
k++;}
g<<k;
f.close();
g.close();
return 0;}