AtCoder Petrozavodsk Contest 001 A

Time limit : 2sec / Memory limit : 256MB

Score : 100 points

Problem Statement

You are given positive integers X and Y. If there exists a positive integer not greater than 10¹⁸ that is a multiple of X but not a multiple of Y, choose one such integer and print it. If it does not exist, print −1.

Constraints

• 1≤X,Y≤10⁹
• X and Y are integers.

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Input

Input is given from Standard Input in the following format:

X Y

Output

Print a positive integer not greater than 10¹⁸ that is a multiple of X but not a multiple of Y, or print −1 if it does not exist.

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Sample Input 1

Copy

8 6

Sample Output 1

Copy

16

For example, 16 is a multiple of 8 but not a multiple of 6.

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Sample Input 2

Copy

3 3

Sample Output 2

Copy

-1

A multiple of 3 is a multiple of 3.

只需要判断x是否是y的倍数。

代码：

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iomanip>
using namespace std;
int a,b;
int main()
{
    cin>>a>>b;
    if(a % b)cout<<a;
    else cout<<-1;
}