q,t = map(int,input().split())
s = list(input().split())
l,r = 0,10**18
for i in range(70):
    mid = (l+r)//2
    st = []
    for j in s:
        if j == '+':
            x = st.pop()
            y = st.pop()
            st.append(x+y)
        elif j == 'max':
            x = st.pop()
            y = st.pop()
            st.append(max(x,y))
        elif j == 'min':
            x = st.pop()
            y = st.pop()
            st.append(min(x,y))
        elif j == 'X':
            st.append(mid)
        else:
            st.append(int(j))
    if st[0] < t:
        l = mid
    else:
        r = mid
    #print(l,r,st[0])
    if i != 69:
        continue
    mid = r
    st = []
    for j in s:
        if j == '+':
            x = st.pop()
            y = st.pop()
            st.append(x+y)
        elif j == 'max':
            x = st.pop()
            y = st.pop()
            st.append(max(x,y))
        elif j == 'min':
            x = st.pop()
            y = st.pop()
            st.append(min(x,y))
        elif j == 'X':
            st.append(mid)
        else:
            st.append(int(j))
    if st[0] == t:
        print(r)
    else:
        print(-1)