input: Write a Python function to determine the maximum value of k where k % x equals y.
  assert find_largest_k(15, 10, 5) == 15
  assert find_largest_k(187, 10, 5) == 185
  assert find_largest_k(16, 11, 1) == 12
output: def find_largest_k(n, x, y):
      return n - (n - y) % x