q, y = map(int, input().split())
s = input().split()
l = -1
r = y + 2

def solve(x):
    stack = []
    for i in range(q):
        if s[i] == "X":
            stack.append(x)
        elif s[i] == "+":
            a = stack.pop()
            b = stack.pop()
            stack.append(a + b)
        elif s[i] == "min":
            a = stack.pop()
            b = stack.pop()
            stack.append(min(a, b))
        elif s[i] == "max":
            a = stack.pop()
            b = stack.pop()
            stack.append(max(a, b))
        else:
            stack.append(int(s[i]))
    return stack[0]

while r-l > 1:
    x = (l + r) >> 1
    if solve(x) >= y: r = x
    else: l = x

if solve(r) == y:
    print(r)
else:
    print(-1)