15th Iberoamerican Mathematical Olympiad Problems 2000

15th Iberoamerican Mathematical Olympiad Problems 2000A1.  Label the vertices of a regular n-gon from 1 to n > 3. Draw all the diagonals. Show that if n is odd then we can label each side and diagonal with a number from 1 to n different from the labels of its endpoints so that at each vertex the sides and diagonals all have different labels.