import sys
input = sys.stdin.readline
from collections import *

N = int(input())
A = list(input().split())
q = deque([])

for Ai in A:
    if Ai=='+':
        a = q.pop()
        b = q.pop()
        q.append(a+b)
    elif Ai=='-':
        a = q.pop()
        b = q.pop()
        q.append(b-a)
    else:
        q.append(int(Ai))
    
print(q[0])