N = int(input())
A = list(map(str, input().split()))
Numbers = []
for i in range(N):
	try:
		Numbers.append(int(A[i]))
	except:
		Second = Numbers.pop()
		First = Numbers.pop()
		if A[i] == "+":
			Numbers.append(First + Second)
		else:
			Numbers.append(First - Second)
print(Numbers.pop())