from collections import deque
from operator import __add__

def calc(X):
	A=deque()
	for op in S:
		A.append(op)
		if op[0] in "_m":
			A.append(str(eval("{0}({1},{2})".format(A.pop(),A.pop(),A.pop()))))
	return int(A[0])
	
Q,Y=map(int,input().split())
S=input().split()
for i in range(Q):
	if S[i]=="+":
		S[i]="__add__"
ok=1<<60
ng=-1
while ok-ng>1:
	mid=(ok+ng)//2
	if calc(mid)>=Y:
		ok=mid
	else:
		ng=mid
print(ok if calc(ok)==Y else -1)