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

def calc(x):
    ANS=[]
    for s in S:
        if s=="X":
            ANS.append(x)
        elif s=="+":
            k=ANS.pop()
            l=ANS.pop()
            ANS.append(k+l)
        elif s=="max":
            k=ANS.pop()
            l=ANS.pop()
            ANS.append(max(k,l))
        elif s=="min":
            k=ANS.pop()
            l=ANS.pop()
            ANS.append(min(k,l))
        else:
            u=int(s)
            ANS.append(u)

    return ANS[-1]

if calc(0)==Y:
    print(0)
    exit()
elif calc(0)>Y:
    print(-1)
    exit()

OK=0
NG=10**18

while NG>OK+1:
    mid=(OK+NG)//2

    if calc(mid)<Y:
        OK=mid
    else:
        NG=mid

if calc(OK)==Y:
    print(OK)
elif calc(NG)==Y:
    print(NG)
else:
    print(-1)