# LPSolverで挑戦するも失敗
# from pulp import LpProblem, LpVariable, LpMinimize, value, PULP_CBC_CMD, LpInteger
# _,y=map(int,input().split())
# s=list(input().split())
# sk=[]
# op = {'+': lambda x,y: f"({x}+{y})",
#       'max': lambda x,y: f"max({x},{y})",
#       'min': lambda x,y: f"min({x},{y})"}
# prob=LpProblem(sense=LpMinimize)
# for t in s:
#     if t in op:
#         b,a=sk.pop(),sk.pop()
#         sk.append(op[t](a,b))
#     else: sk.append(t)
# print(sk[0])
# x=LpVariable("x",lowBound=0,cat=LpInteger)
# prob+=eval(sk[0],{"X":x,
#                   "max": lambda a,b: a if a>=b else b,
#                   "min": lambda a,b: a if a<=b else b})==y
# prob+=x
# prob.solve(PULP_CBC_CMD(msg=False))
# if prob.status!=1: print(-1)
# else: print(int(value(x)))

_,y=map(int,input().split())
s=list(input().split())
sk=[]
op = {'+': lambda x,y: f"({x}+{y})",
      'max': lambda x,y: f"max({x},{y})",
      'min': lambda x,y: f"min({x},{y})"}
for t in s:
    if t in op:
        b,a=sk.pop(),sk.pop()
        sk.append(op[t](a,b))
    else: sk.append(t)
# print(sk[0])
def f(x): return eval(sk[0],{"X":x,
                   "max": lambda a,b: a if a>=b else b,
                   "min": lambda a,b: a if a<=b else b})
ok,ng=(1<<61)-1,-1
while abs(ok-ng)>1:
    x=(ok+ng)//2
    if f(x)>=y: ok=x
    else: ng=x
print(ok if f(ok)==y else -1)