#include <stdio.h>
int n;
char x[2000001];
int i,c,k;
int ciur(int n)
{
     for(i=2;i<=n;i++) x[i]=1;
     for(i=2;i<=n;i++)
     {
                      if (x[i]!=0)
                      {
                                  c=i;
                                  while(c<=n)
                                  {
                                             x[c]=0;
                                             c+=i;
                                  }
                                  k++;
                      }
     }
                      
     return k;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    printf("%d",ciur(n));
    return 0;
}