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

def check(n):
    stack = []
    for i in S:
        if(i == "+"):
            stack.append(stack.pop()+stack.pop())
        elif(i == "min"):
            stack.append(min(stack.pop(),stack.pop()))
        elif(i == "max"):
            stack.append(max(stack.pop(),stack.pop()))
        elif(i == "X"):
            stack.append(n)
        else:
            stack.append(int(i))
    return stack[0] >= Y

def last_check(n):
    stack = []
    for i in S:
        if(i == "+"):
            stack.append(stack.pop()+stack.pop())
        elif(i == "min"):
            stack.append(min(stack.pop(),stack.pop()))
        elif(i == "max"):
            stack.append(max(stack.pop(),stack.pop()))
        elif(i == "X"):
            stack.append(n)
        else:
            stack.append(int(i))
    return stack[0] == Y

ng,ok = -1,10**18
while(ok - ng > 1):
    mid = (ok+ng)//2
    if(check(mid)):
        ok = mid
    else:
        ng = mid

print(ok if last_check(ok) else -1)