import sys
mod = 998244353
mod2 = 10**9+7

Q, Y = map(int, input().split())
s = list(input().split())
def f(x):
    A = []
    for i in s:
        if i == "+":
            A.append(A.pop()+A.pop())
        elif i == "min":
            A.append(min(A.pop(), A.pop()))
        elif i == "max":
            A.append(max(A.pop(), A.pop()))
        else:
            if i == "X":
                A.append(x)
            else:
                A.append(int(i))
    return A[0]
ng, ok = -1, 1<<60
while ok - ng > 1:
    m = (ok+ng) // 2
    if f(m) >= Y:ok = m
    else:ng = m
print(ok if ok < 1<<60 and f(ok) == Y else -1)