A9580 | Dreamoon and Stairs
时间限制1s
内存限制256MB
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题目描述
Dreamoon wants to climb up a stair of $n$ steps. He can climb $1$ or $2$ steps at each move. Dreamoon wants the number of moves to be a multiple of an integer $m$ .
What is the minimal number of moves making him climb to the top of the stairs that satisfies his condition?
What is the minimal number of moves making him climb to the top of the stairs that satisfies his condition?
输入格式
The single line contains two space separated integers $n$ , $m$ ( $0<n<=10000,1<m<=10$ ).
输出格式
Print a single integer — the minimal number of moves being a multiple of $m$ . If there is no way he can climb satisfying condition print $-1$ instead.
输入输出样例
输入 #1
10 2
输出 #1
6
输入 #2
3 5
输出 #2
-1
For the first sample, Dreamoon could climb in 6 moves with following sequence of steps: {2, 2, 2, 2, 1, 1}.
For the second sample, there are only three valid sequence of steps {2, 1}, {1, 2}, {1, 1, 1} with 2, 2, and 3 steps respectively. All these numbers are not multiples of 5.
For the second sample, there are only three valid sequence of steps {2, 1}, {1, 2}, {1, 1, 1} with 2, 2, and 3 steps respectively. All these numbers are not multiples of 5.
C++ 编辑器
输入
输出
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评测结果：Accepted