哎……只差一个证明就够称为“解题报告”了……

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SGU126 解题手记

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//AC
#include <iostream>
using namespace std;
 
long gcd(long a,long b)
{
    long t;
    while (b)
    {
        t=a; a=b; b=t%b;
    }
    return a;
}
 
long log2(long a)
{
    int i=0;
    for (;a>1;++i,a>>=1);
    return i;
}
 
int main()
{
    long a,b,t;
    cin>>a>>b;
    if (a>0 && b>0)
    {
        t=(a+b)/gcd(a,b);
        if ((t-1)&t) cout<<-1;
        else cout<<log2(t);
    }
    else cout<<0;
    cout<<endl;
}