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

inf = 1<<60

ok = inf
ng = -1
ans = None
while ok-ng > 1:
    X = (ok+ng)//2
    A = []
    for s in S:
        if s.isdecimal():
            A.append(int(s))
        elif s == "X":
            A.append(X)
        elif s == "+":
            A[-2] += A[-1]
            A.pop()
        elif s == "min":
            A[-2] = min(A[-2],A[-1])
            A.pop()
        elif s == "max":
            A[-2] = max(A[-2],A[-1])
            A.pop()
    
    if A[0] >= Y:
        ok = X
        ans = A[0]
    else:
        ng = X

if abs(ok) == inf:
    print(-1)
else:
    if ans == Y:
        print(ok)
    else:
        print(-1)