import sys
input = sys.stdin.readline
def read_values(): return map(int, input().split())
def read_list(): return list(read_values())
 

def main():
    q,y=read_values()
    s=input().split()
    l=-1
    r=10**15
    las=-1
    while l+1<r:
        m=(l+r)//2
        a=list()
        for v in s:
            if v == "X":
                a.append(m)
            elif v == "min":
                add = min(a[-1],a[-2])
                a.pop()
                a.pop()
                a.append(add)
            elif v == "max":
                add = max(a[-1],a[-2])
                a.pop()
                a.pop()
                a.append(add)
            elif v == "+":
                add = a[-1]+a[-2]
                a.pop()
                a.pop()
                a.append(add)
            else:
                a.append(int(v))
        if a[0] < y:
            l=m
        else:
            r=m
            las=a[0]

    if las==y:
        print(r)
    else:
        print(-1)
        
if __name__ == "__main__":
    main()