import sys
sys.set_int_max_str_digits(0)

N = int(input())
A = list(input().split())

for i in range(N):
    if not (A[i] == '+' or A[i] == '-'):
        A[i] = int(A[i])
stack = []
for a in A:
    if a == '+':
        y, x = stack.pop(), stack.pop()
        sub = x + y
    elif a == '-':
        y, x = stack.pop(), stack.pop()
        sub = x - y
    else:
        sub = a
    stack.append(sub)

print(stack.pop())