If at first you don't succeed...

题意翻译

有$N$个人参加了考试。考试完成后，在通过的人中，有$A$个人去了第一个酒店聚会，有$B$个人去了第二个酒店聚会，有$C$个人同时去了两个酒店聚会。 问有多少个人没有通过考试（至少有一个，因为主角没有通过考试） 感谢@attack 提供翻译

题目描述

Each student eagerly awaits the day he would pass the exams successfully. Thus, Vasya was ready to celebrate, but, alas, he didn't pass it. However, many of Vasya's fellow students from the same group were more successful and celebrated after the exam. Some of them celebrated in the BugDonalds restaurant, some of them — in the BeaverKing restaurant, the most successful ones were fast enough to celebrate in both of restaurants. Students which didn't pass the exam didn't celebrate in any of those restaurants and elected to stay home to prepare for their reexamination. However, this quickly bored Vasya and he started checking celebration photos on the Kilogramm. He found out that, in total, BugDonalds was visited by $ A $ students, BeaverKing — by $ B $ students and $ C $ students visited both restaurants. Vasya also knows that there are $ N $ students in his group. Based on this info, Vasya wants to determine either if his data contradicts itself or, if it doesn't, how many students in his group didn't pass the exam. Can you help him so he won't waste his valuable preparation time?

输入输出格式

输入格式

The first line contains four integers — $ A $ , $ B $ , $ C $ and $ N $ ( $ 0 \leq A, B, C, N \leq 100 $ ).

输出格式

If a distribution of $ N $ students exists in which $ A $ students visited BugDonalds, $ B $ — BeaverKing, $ C $ — both of the restaurants and at least one student is left home (it is known that Vasya didn't pass the exam and stayed at home), output one integer — amount of students (including Vasya) who did not pass the exam. If such a distribution does not exist and Vasya made a mistake while determining the numbers $ A $ , $ B $ , $ C $ or $ N $ (as in samples 2 and 3), output $ -1 $ .

输入输出样例

输入样例 #1

10 10 5 20

输出样例 #1

5

输入样例 #2

2 2 0 4

输出样例 #2

-1

输入样例 #3

2 2 2 1

输出样例 #3

-1

说明

The first sample describes following situation: $ 5 $ only visited BugDonalds, $ 5 $ students only visited BeaverKing, $ 5 $ visited both of them and $ 5 $ students (including Vasya) didn't pass the exam. In the second sample $ 2 $ students only visited BugDonalds and $ 2 $ only visited BeaverKing, but that means all $ 4 $ students in group passed the exam which contradicts the fact that Vasya didn't pass meaning that this situation is impossible. The third sample describes a situation where $ 2 $ students visited BugDonalds but the group has only $ 1 $ which makes it clearly impossible.