input: Write a python function to compute the fitness of a given chromosome in the TSP problem.
  assert fitness([0, 2, 1, 3])==2207
  assert fitness([1, 3, 0, 2])==2344
  assert fitness([2, 0, 3, 1])==2503
output: def fitness(chromosome):
      distance_matrix = [
          [0, 1312, 1386, 2381],
          [1312, 0, 2344, 1000],
          [1386, 2344, 0, 1117],
          [2381, 1000, 1117, 0]
      ]
      total_distance = 0
      for i in range(len(chromosome)):
          total_distance += distance_matrix[chromosome[i-1]][chromosome[i]]
      return total_distance