#include <bits/stdc++.h>

using namespace std;
using ll = long long;

vector<ll> factor;

void all_factor(ll n){
    factor.clear();
    for (ll i = 1; i*i <= n; i++){
        if (n % i == 0){
            factor.push_back(i);
            if (i*i != n) factor.push_back(n / i);
        }
    }
}

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    ll A, B, mi=2e9;
    cin >> A >> B;
    all_factor(B-A);

    for (auto x : factor){
        if (x > A) mi = min(mi, x);
    }

    if (mi == 2e9) mi = A-1;
    cout << mi-A << '\n';

    return 0;
}