n = int(input())
tokens = input().split()
stack = []

for token in tokens:
    if token in "+-":
        b = stack.pop()
        a = stack.pop()
        if token == '+':
            stack.append(a + b)
        else:
            stack.append(a - b)
    else:
        stack.append(int(token))

print(stack[0])