Q, Y = (int(x) for x in input().split())
s = list(map(str, input().split()))

def calc(x):
    stack = []
    for j in s:
        if j == "X":
            stack.append(x)
        elif j == "+":
            a = stack.pop()
            b = stack.pop()
            stack.append(a+b)
        elif j == "max":
            a = stack.pop()
            b = stack.pop()
            stack.append(max(a, b))
        elif j == "min":
            a = stack.pop()
            b = stack.pop()
            stack.append(min(a, b))
        else:
            stack.append(int(j))
    return stack[-1]


left, right = -1, 10**20
while left + 1 < right:
    mid = (left+right)//2
    if calc(mid) < Y:
        left = mid
    else:
        right = mid

if calc(right) == Y:
    print(right)
else:
    print(-1)