def main():
    N = int(input())
    A = input().split()

    stack = []
    for elm in A:
        match elm:
            case "+":
                elm2 = stack.pop()
                elm1 = stack.pop()
                stack.append(elm1 + elm2)
            case "-":
                elm2 = stack.pop()
                elm1 = stack.pop()
                stack.append(elm1 - elm2)
            case num:
                stack.append(int(num))

    assert len(stack) == 1
    print(stack[0])


if __name__ == "__main__":
    main()