#include<stdio.h>
#include<stdlib.h>
bool *v;
int main()
  {register int n,nr=0,i,j;
   freopen("ciur.in","rt",stdin);
   freopen("ciur.out","wt",stdout);
   scanf("%d",&n); v=(bool*)calloc(n+1,sizeof(n));
   for(i=2;i<=n;++i)
      if(!v[i])
        {++nr;
         for(j=2;j*i<=n;++j) v[j*i]=1;
        }
   printf("%d\n",nr);
   free(v);
   //system("PAUSE>NULL");
   return 0;
  }