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给定正整数 $n, r$，求
第一行一个数 $T$，表示有 $T$ 组测试数据。
接下来 $T$ 行，每行两个正整数 $n, r$。
输出 $T$ 行，每行一个整数表示答案。
3 3 5 3 6 3 7
3 1 -1
对于 30% 的数据，满足 $n \leq 10^5, r \leq 10^2, T \leq 10$；
对于 60% 的数据，满足 $n \leq 10^7, r \leq 10^3, T \leq 10^2$；
对于 100% 的数据，满足 $n \leq 10^9, r \leq 10^4, T \leq 10^4$。
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