q,y=map(int,input().split())
S=input().split()
def f(n):
    E=["+", "min", "max"]
    stc=[]
    for i in S:
        if i in E:
            c=E.index(i)
            if c==0:
                a=stc.pop()
                b=stc.pop()
                stc.append(a+b)
            elif c==1:
                a = stc.pop()
                b = stc.pop()
                stc.append(min(a,b))
            else:
                a = stc.pop()
                b = stc.pop()
                stc.append(max(a, b))
        else:
            if i=="X":
                stc.append(n)
            else:
                stc.append(int(i))
    return stc[0]
l,r=0,10**18
if f(0)>y or f(r)<y:
    print(-1)
    exit()
elif f(0)==y:
    print(0)
    exit()
while r-l>1:
    c=(l+r)//2
    if f(c)>=y:
        r=c
    else:
        l=c
if f(r)==y:
    print(r)
else:
    print(-1)