#include <stdio.h>

main()
{
  int i, n;
  double r, s;

  printf("Input Number\n"); 
  scanf( "%d", &n );

  if(n>0)
    {
      s=0.0 ;
      i=1   ;
      while(i<=n)
	{
          printf("Input r[%d]\n", i );
          scanf("%lf", &r );
          s=s+1.0/r;
	  i=i+1;
	}
      printf("Total resistance =%f\n", 1.0/s );
    }else{
      printf("Illegal Number\n");
    }
}