n = int(input())
a = input().split()
stack = []
for i in a:
    if i not in ["+", "-"]:
        stack.append(int(i))
    else:
        c = stack.pop()
        b = stack.pop()
        if i == "+":
            stack.append(b + c)
        else:
            stack.append(b - c)
print(stack[0])