Q, Y = map(int,input().split())
S = input().split()
code = {"+":0,"min":1,"max":2}

def f(x):
    stack = []
    for s in S:
        if s.isdigit():
            stack.append(int(s))
        elif s == "X":
            stack.append(x)
        else:
            a = stack.pop()
            b = stack.pop()
            match code[s]:
                case 0:
                    stack.append(a + b)
                case 1:
                    stack.append(min(a,b))
                case 2:
                    stack.append(max(a,b))
        dum = 0
    return stack[0]

lb = -1
ub = Y
while ub - lb > 1:
    mid = (ub + lb) // 2
    if f(mid) >= Y:
        ub = mid
    else:
        lb = mid
if f(ub) == Y:
    print(ub)
else:
    print(-1)