1 #include<iostream>
 2 #include<cstring>
 3 #include<cstdlib>
 4 #include<cstdio>
 5 #include<algorithm>
 6 #include<cmath>
 7 #include<queue>
 8 #include<map>
 9 #include<set>
10 #include<string>
11 //#include<pair>
12 
13 #define N 1005
14 #define M 1000005
15 #define mod 1000000007
16 #define inf 0x3f3f3f3f
17 //#define p 10000007
18 #define mod2 100000000
19 #define ll long long
20 #define LL long long
21 #define maxi(a,b) (a)>(b)? (a) : (b)
22 #define mini(a,b) (a)<(b)? (a) : (b)
23 
24 using namespace std;
25 
26 ll mul=3628800;
27 ll x,y;
28 ll ans;
29 ll tmi,tma;
30 ll dmi,dma;
31 ll dan;
32 ll num,tot;
33 
34 void ini()
35 {
36     ans=0;
37     tmi=y*mul;
38     tma=(y+1)*mul;
39     dmi=tmi/x;
40     dma=tma/x;
41     num=1;
42     dan=mul;
43     tot=mul;
44 }
45 
46 
47 void solve()
48 {
49     ans=x-1;
50     ll k1,k2;
51     ll te;
52     if(dan>=dma){
53         ans=-1;return;
54     }
55     for(num=1;num<=x;num++){
56         te=mul/num;
57         if(dan>=dmi) break;
58         k1=(dmi-dan+te-1)/te;
59         k2=(dma-dan+te-1)/te;
60       //  printf(" num=%I64d ans=%I64d dan=%I64d dmi=%I64d dma=%I64d te=%I64d k1=%I64d k2=%I64d\n",
61 //               num,ans,dan,dmi,dma,te,k1,k2);
62         if(k1!=k2){
63             ans+=k1;
64             dan+=k1*mul/num;
65             return;
66         }
67         else{
68             dan+=(k1-1)*te;
69             ans+=(k1-1);
70         }
71     }
72 }
73 
74 void out()
75 {
76     printf("%I64d\n",ans);
77 }
78 
79 int main()
80 {
81     //freopen("data.in","r",stdin);
82     //freopen("data.out","w",stdout);
83     //scanf("%d",&T);
84    // for(int ccnt=1;ccnt<=T;ccnt++)
85    // while(T--)
86     while(scanf("%I64d%I64d",&x,&y)!=EOF)
87     {
88         //if(n==0 && k==0 ) break;
89         //printf("Case %d: ",ccnt);
90         ini();
91         solve();
92         out();
93     }
94 
95     return 0;
96 }