n=int(input())
a=list(input().split())
stack=[]
for i in a:
    if i.isdecimal():
        stack.append(int(i))
    elif i=="+":
        x=stack.pop()
        y=stack.pop()
        stack.append(x+y)
    else:
        x=stack.pop()
        y=stack.pop()
        stack.append(x-y)
print(stack[0])