def Bisect_Int(ok,ng,is_ok):
    while abs(ok-ng)>1:
        mid=(ok+ng)//2
        if is_ok(mid):
            ok=mid
        else:
            ng=mid
    return ok

Q,Y=map(int,input().split())
S=input().split()
def f(x):
    queue=[]
    for s in S:
        if s=="+":
            queue.append(queue.pop()+queue.pop())
        elif s=="min":
            queue.append(min(queue.pop(),queue.pop()))
        elif s=="max":
            queue.append(max(queue.pop(),queue.pop()))
        elif s=="X":
            queue.append(x)
        else:
            queue.append(int(s))
    return queue[0]
def is_ok(x):
    return f(x)>=Y
ans=Bisect_Int(1<<60,-1,is_ok)
if f(ans)!=Y:
    ans=-1
print(ans)