2018牛客多校训练----max

链接：https://www.nowcoder.com/acm/contest/143/G
来源：牛客网
 

题目描述

Give two positive integer c, n. You need to find a pair of integer (a,b) satisfy 1<=a,b<=n and the greatest common division of a and b is c.And you need to maximize the product of a and b

输入描述:

The first line has two positive integer c,n

输出描述:

Output the maximum product of a and b.

If there are no such a and b, just output -1

示例1

输入

2 4

输出

8

说明

a=2,b=4

备注:

1<=c,n<=10^9

  给出两个数n,k,找出满足a<=n,b<=n的一对数a和b使a*b最大。

#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

int main()
{
    ll c,n,ans,a,b;
    scanf("%lld%lld",&c,&n);
    if(c>n)
        printf("-1\n");
    else
    {
        a=n/c;
        b=n/c-1;
        if(a==1)
            b=1;
        ans=a*b*c*c;
    }
    printf("%lld\n",ans);
    return 0;
}