Codeforces Round #554 (Div. 2) C

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=1e5+7;
const int mod=1e9+7;
int fac[maxn],tot=0;
ll a,b;
ll gcd(ll a,ll b)
{
    return b==0?a:gcd(b,a%b);
}
void solve(ll x)
{
    for(ll i=1;i*i<=x;i++)
    {
        if(x%i==0)
        {
            fac[tot++]=i;
            if(i!=x/i)fac[tot++]=x/i;
        }
    }
}
int main()
{
    
    scanf("%lld%lld",&a,&b);
    if(a>b)swap(a,b);
    solve(b-a);
    ll minn=a*b/gcd(a,b),out=0;
    for(int i=0;i<tot;i++){
        ll res=a+(fac[i]-a%fac[i])%fac[i];
        res=(res)*(b+(fac[i]-a%fac[i])%fac[i])/gcd(b-a,res);
        if(res<minn)
        {
            minn=res;
            out=(fac[i]-a%fac[i])%fac[i];
        }
    }
    cout<<out<<endl;
    return 0;
}