#include<cstdio>
#include<cmath>
using namespace std;

int n,nr;
char V[2000000];

int main()
{
 int i,j;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);

 for(i=2;i<=sqrt(n);++i)
   {
       if(!V[i])
     {
         j=2;
       while(i*j<=n)
        {
            V[i*j]='1';
            ++j;
            } }
       }

for(int i=2;i<=n;++i)
{
if(!V[i])
++nr;
}
 printf("%d",nr);
return 0;
}