n = int(input())
lst = list(input().split())
num_s = []
for a in lst:
    if a.isnumeric():
        num_s.append(int(a))
    elif a == "+":
        n1 = num_s.pop(-1)
        n2 = num_s.pop(-1)
        num_s.append(n1 + n2)
    else:
        n1 = num_s.pop(-1)
        n2 = num_s.pop(-1)
        num_s.append(n2 - n1)
print(num_s[0])