// // Created by yamunaku on 2020/02/11. // #include <bits/stdc++.h> using namespace std; #define rep(i, n) for(int i = 0; i < (n); i++) #define repl(i, l, r) for(int i = (l); i < (r); i++) #define per(i, n) for(int i = ((n)-1); i >= 0; i--) #define perl(i, l, r) for(int i = ((r)-1); i >= (l); i--) #define all(x) (x).begin(),(x).end() #define MOD9 998244353 #define MOD1 1000000007 #define IINF 1000000000 #define LINF 1000000000000000000 #define SP <<" "<< #define CYES cout<<"Yes"<<endl #define CNO cout<<"No"<<endl #define CFS cin.tie(0);ios::sync_with_stdio(false) #define CST(x) cout<<fixed<<setprecision(x) using ll = long long; using ld = long double; using vi = vector<int>; using mti = vector<vector<int>>; using vl = vector<ll>; using mtl = vector<vector<ll>>; using pi = pair<int, int>; using pl = pair<ll, ll>; template<typename T> using heap = priority_queue<T, vector<T>, function<bool(const T, const T)>>; int main(){ // CFS; int a, b; cin >> a >> b; repl(i, 2, 101){ if(a % i == 0 && b % i == 0){ cout << -1 << endl; return 0; } } int ans = 0; rep(i, 100000){ rep(j, 101){ if(i-a*j>=0&&(i-a*j)%b==0){ goto next; } } ans++; next:; } cout << ans << endl; return 0; }