1 #include<cstdio>
2 #include<queue>
3 #include<cstring>
4 #include<cmath>
5 using namespace std;
6 int n,x,y;
7 bool v[20000];
8 struct point
9 {
10 int x;
11 int step;
12 };
13
14 int change(int x,int y,int z)
15 {
16 if (z==4) return (x/10)*10+y;
17 else if (z==3)
18 {
19 int t=y*10+x%10;
20 return (x/100)*100+t;
21 }
22 else if (z==2)
23 {
24 int t=y*100+x%100;
25 return (x/1000)*1000+t;
26 }
27 else if (z==1)
28 {
29 return y*1000+(x%1000);
30 }
31 }
32
33 bool prime(int x)
34 {
35 if (x==2 || x==3) return true;
36 if (x<=1 || x%2==0) return false;
37 for (int i=3;i<=sqrt(x);i++)
38 if (x%i==0) return false;
39 return true;
40 }
41
42 void bfs(int sx,int ex)
43 {
44 memset(v,0,sizeof(v));
45 queue<point>que;
46 point now,next;
47 now.x=sx;
48 now.step=0;
49 v[sx]=1;
50 que.push(now);
51 while (!que.empty())
52 {
53 now=que.front();
54 que.pop();
55 if (now.x==ex)
56 {
57 printf("%d\n",now.step);
58 return ;
59 }
60
61 for (int i=0;i<=9;i++)
62 for (int j=1;j<=4;j++)
63 {
64 if (i==0 && j==1) continue;
65 next.x=change(now.x,i,j);
66 if (prime(next.x) && !v[next.x])
67 {
68 v[next.x]=1;
69 next.step=now.step+1;
70 que.push(next);
71 }
72 }
73
74 }
75 printf("Impossible\n");
76 }
77 int main()
78 {
79 scanf("%d",&n);
80 for (int t=1;t<=n;t++)
81 {
82 scanf("%d%d",&x,&y);
83 bfs(x,y);
84 }
85 return 0;
86 }
