n = int(input())
l = input().split()
i = 0
while i != n:
  if l[i] in '+-':
    l[i] = str(eval(l[i-2]+l[i]+l[i-1]))
    l.pop(i-2)
    l.pop(i-2)
    i-=2
    n-=2
  i+=1
print(l[0])