#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<math.h>
using namespace std;
#define mod (1000000000+7)
#define N (10007)
#define INF 1e16
typedef long long ll;
typedef pair<ll,ll> P;

ll gcd(ll a,ll b){
    if(a<b)swap(a,b);
    if(a%b==0)return b;
    else return gcd(b,a%b);
}

int main(void){
    ll a,b;
    cin>>a>>b;
    ll g = gcd(a,b);
    //cout<<g<<endl;
    ll ans = 0;
    if(g != 1)cout<<-1<<endl;
    else{
        if(a>b)swap(a,b);
        for(ll i=0;i<a;i++){
            ll tmp = b*i;
            ll r = tmp%a;
            ans += (tmp-r)/a;
        }
        cout<<ans<<endl;
    }
	return 0; 
}