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

def solve(x):
    A=[]
    for i in S:
        if i=='+':
            A.append(A.pop()+A.pop())
        elif i=='min':
            A.append(min(A.pop(),A.pop()))
        elif i=='max':
            A.append(max(A.pop(),A.pop()))
        elif i=='X':
            A.append(x)
        else:
            A.append(int(i))
    return A[0]

if solve(10**15)<Y:
    print(-1)
    exit()

if solve(0)>Y:
    print(-1)
    exit()

d=[-1,10**15]
while d[1]-d[0]>1:
    md=sum(d)//2
    r=solve(md)
    if r>=Y:
        d[1]=md
    else:
        d[0]=md
    
if solve(d[1])==Y:
    print(d[1])
else:
    print(-1)