PROBLEM C
Optimisation

Input File Name: C.DAT
Source File Name:C.PAS or C.C or C.CPP

	A company decides to simulate on computer the process of manufacturing its own goods. 
In order to do that, it makes the following observations:
	1. The whole process can be splitted into several steps; between them there are some 
dependencies. This can be represented by a diagram (graph), which we suppose to be only one 
for all goods produced by company as in figure 1;
	2. First step designates the start of manufacturing process;there is only one first step, 
denoted by the number 1;
	3. There are not steps isolated or outside the process (every step is linked by a path with 
the first step);
	4. Some steps are total dependants; so, we claim that the step i is total dependant of step j 
if every path in the fabrication process cannot arrive to i without was passing through j.
	So, all steps are total dependants of step 1.

	Example: In the process shown by the figure 1 the step 4 is total dependant of step 3, 
steps 5,6 and 7 are total dependants of 4 (hence of 3), but step 3 is not total dependant of step 2.

	The Computing Center Dept. of company notes that whole manufacturing process is 
easier to be controlled if it would be structured by a tree, as follows:
	- All steps of manufacturing process are nodes of the tree;
	- Each node ensures total dependence of all its own descendants; 

	The tree associated to the diagram from figure 1 is shown in figure 2.

	Your task is to write a program that builds this dependence tree.
	Input:
	The input file contains several input data sets. An input data set has the following format:
n- number of steps of manufacturing process (2<=n<=99);
a11 a12 ... a1n
a21 a22 ... a2n
...............
an1 an2 ... ann
	where aij=1 if step j follows directly step i in the process diagram, otherwise aij=0.
	Output:
	At output, the program must write n-1 lines for every input data set; each line has the 
format:
i j
with the meaning that node j is a direct descendant of node i in the tree.
	The pair (i1 j1) follows (i2 j2) if and only if (i1