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

stack = []
for i in S:
  if i == "X" or (i != "max" and i != "min" and i != "+"):
    stack.append(i)
  else:
    p = stack.pop()
    q = stack.pop()
    if i == "+":
      stack.append(p + i + q)
    else:
      stack.append(i + "(" + p + "," + q + ")")

que = stack[-1]
for i in range(5 * 10 ** 5):
  que2 = que.replace("X", str(i))
  if eval(que2) == Y:
    print(i)
    exit()

print(-1)