import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

n = I()
a = LS()

stack = []

for i in a:
    if i in "+-":
        y = stack.pop()
        x = stack.pop()
        if i == "+":
            stack.append(x+y)
        else:
            stack.append(x-y)
    else:
        stack.append(int(i))

print(stack[0])