#include<stdio.h>

int main()
  {
   freopen("ciur.in","r",stdin);
   freopen("ciur.out","w",stdout);
   long n,i,j;
   char prim[2000005];
   scanf("%li",&n);
   for(i=2;i<=n;i++)
      prim[i]=1;
   long nr=0;
   for(i=2;i<=n;i++)
     if (prim[i]) 
        {
         nr++;
         for(j=i+i;j<=n;j+=i)
            prim[j]=0;
        }
   printf("%li",nr);   
   return 0;
  }