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