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

def func(x):
    stack = []
    for op in S:
        if op == "+":
            a, b = int(stack.pop()), int(stack.pop())
            stack.append(a+b)
        elif op == "min":
            a, b = int(stack.pop()), int(stack.pop())
            stack.append(min(a, b))
        elif op == "max":
            a, b = int(stack.pop()), int(stack.pop())
            stack.append(max(a, b))
        elif op == "X":
            stack.append(x)
        else:
            stack.append(int(op))
    return stack[0]

INF = 10**18
minus = func(-INF)
plus = func(INF)

if Y < minus or plus < Y:
    exit(print(-1))

left = -INF
right = INF
while left+1 < right:
    mid = (left+right)//2
    if func(mid) < Y:
        left = mid
    else:
        right = mid

if func(right) == Y:
    if right >= 0:
        print(right)
    elif func(0) == Y:
        print(0)
    else:
        print(-1)
else:
    print(-1)