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

def is_ok(x):
    if x < 0: return False
    stack = []
    for s in S:
        if s in ('+','min','max'):
            a = stack.pop()
            b = stack.pop()
            if s == '+':
                c = a+b
            elif s == 'min':
                c = min(a,b)
            else:
                c = max(a,b)
            stack.append(c)
        elif s == 'X':
            stack.append(x)
        else:
            stack.append(int(s))
    v = stack.pop()
    return v >= Y, v

ng = -1
ok = 10**24
while ok - ng > 1:
    mid = (ok+ng)//2
    if is_ok(mid)[0]:
        ok = mid
    else:
        ng = mid

v = is_ok(ok)[1]
print(ok if v == Y else -1)