#include using namespace std; typedef long long ll; #define REP(i,n) for(int i=0; i #define VLL vector #define VVI vector> #define VVLL vector> #define VC vector #define VS vector #define VVC vector> #define VB vector #define VVB vector> #define fore(i,a) for(auto &i:a) typedef pair P; template bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; } template bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; } const int INF = 1 << 29; const ll INFL = 1LL << 60; const ll mod = 1000000007; int main() { ll a, b; cin >> a >> b; ll c = a + b; ll ans = INFL; for (ll i = 1; i*i <= c; i++) { if (c%i == 0) { if ((a + i) % b == 0 && (b + i) % a == 0) { ans = min(ans, i); } if ((a + (c / i)) % b == 0 && (b + (c / i)) % a == 0) { ans = min(ans, c / i); } } } if (ans == INFL)cout << -1 << endl; else cout << ans << endl; }