import sys
readline=sys.stdin.readline
write=sys.stdout.write
from math import gcd as GCD
import math

N=int(readline())
queue=[]
for a in readline().split():
    if a=="+":
        x=queue.pop()
        queue[-1]+=x
    elif a=="-":
        x=queue.pop()
        queue[-1]-=x
    else:
        a=int(a)
        queue.append(a)
ans=queue[0]
print(ans)