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