t = int(raw_input().strip())
ans = -1

def backtrack (s, k, n, at, coeff, sizes):
  global ans
  if at == k:
    if (n - coeff) % (k + 1): return
    at, total, l, good = 0, 0, (n - coeff) // (k + 1), 1
    for it in sizes:
      l += it
      if l <= 0:
        good = 0
        break
      total += int(s[at : at + l])
      at += l
    if good: ans = min(ans, total)
    return
  sizes.append(0)
  for i in range(-1, 2):
    sizes[-1] = i
    backtrack(s, k, n, at + 1, coeff + (k - at) * i, sizes)
  sizes.pop()

for _ in range(t):
  n, k = map(int, raw_input().strip().split())
  s = raw_input().strip()
  ans = int(s)
  backtrack(s, k, n, 0, 0, [0])
  print ans