Q, Y = map(int, input().split())
S = list(map(str, input().split()))

def solve(S, x):
  stack = []
  for i in S:
    if i == "X" or (i != "max" and i != "min" and i != "+"):
      if i == "X":
        stack.append(x)
      else:
        stack.append(i)
    else:
      p = stack.pop()
      q = stack.pop()
      if i == "+":
        stack.append(int(p) + int(q))
      else:
        if i == "max":
          stack.append(max(int(p), int(q)))
        else:
          stack.append(min(int(p), int(q)))
  return stack[-1]

if "X" not in S:
  if int(solve(S, 0)) == Y:
    print(0)
  else:
    print(-1)
  exit()

left = -1
right = 10 ** 14
while left + 1 < right:
  mid = (left + right) // 2
  res = int(solve(S, mid))
  if res == Y:
    right = mid
  elif res < Y:
    left = mid
  else:
    right = mid

if solve(S, right) == Y:
  print(right)
else:
  print(-1)