text: #include <stdio.h>
  #include <math.h>
  
  void main()
  {
   double x=0.0, y=0.0, one=1.0;
   int i,N;
  
   N = 100000000;
  
   for(i=1;i<=N;i++)
     {
       x += pow((double)i,-2.0);
     }
  
   for(i=N;i>=1;i--)
     {
       y += pow((double)i,-2.0);
     }
  
   printf("[index increasing] sum = %18.16f\n",x);
   printf("[index decreasing] sum = %18.16f\n",y);
  }
  