N,Y = map(int,input().split())
S = list(input().split())
Op = ["+","min","max"]
def f(x):
    A = []
    for i in range(N):
        if S[i] not in Op:
            if S[i]=="X":
                A.append(x)
            else:
                A.append(int(S[i]))
        else:
            a = A.pop()
            b = A.pop()
            if S[i]=="+":
                A.append(a+b)
            elif S[i]=="min":
                A.append(min(a,b))
            else:
                A.append(max(a,b))
    return A[0]
low = -1
high = 10**13+10
while high-low>1:
    mid = (high+low)//2
    if f(mid)>=Y:
        high = mid
    else:
        low = mid
x = high
if f(x)==Y:
    print(x)
else:
    print(-1)