1 #include<cstdio>
 2 #include<cstring>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<iostream>
 6 #include<queue>
 7 #include<string>
 8 #include<cmath>
 9 using namespace std;
10 #define MAXN 10001
11
12 bool prime[MAXN];
13 int vis[MAXN];
14 int a, b, t;
15
16 void deal()
17 {
18     for (int i = 2; i <= MAXN; ++i)
19         if (!prime[i])
20             for (int j = i*i; j <= MAXN; j += i)
21                 prime[j] = true;
22     /*for (int i = 0; i < 50; ++i)
23         if (!prime[i]) cout << i << " ";
24     cout << endl;*/
25 }
26
27 int bfs()
28 {
29     queue<int> q;
30     q.push(a);
31     q.push(-1);
32     int ans = 0;
33     while (!q.empty()) {
34         int t = q.front();
35         if (t == -1) {
36             q.pop();
37             if (q.empty()) return -1;
38             ans++;
39             q.push(t); continue;
40         }q.pop();
41         if (t == b) return ans;
42         int s;
43         for (int i = 1; i <= 9; ++i) {
44             s = i * 1000 + t % 1000;
45             if (!vis[s] && !prime[s]) {
46                 q.push(s);
47                 vis[s] = true;
48             }
49         }
50         for (int i = 0; i <= 9; ++i) {
51             s = i * 100 + t % 100 + t/1000*1000;
52             if (!vis[s] && !prime[s]) {
53                 q.push(s);
54                 vis[s] = true;
55             }
56         }
57         for (int i = 0; i <= 9; ++i) {
58             s = i * 10 + t % 10 + t/100*100;
59             if (!vis[s] && !prime[s]) {
60                 q.push(s);
61                 vis[s] = true;
62             }
63         }
64         for (int i = 0; i <= 9; ++i) {
65             s = i + t / 10 * 10;
66             if (!vis[s] && !prime[s]) {
67                 q.push(s);
68                 vis[s] = true;
69             }
70         }
71     }
72     return -1;
73 }
74
75 int main()
76 {
77     int  t;
78     cin >> t;
79     deal();
80     while (t--) {
81         cin >> a >> b;
82         memset(vis,0,sizeof(vis));
83         int res = bfs();
84         if (res == -1) puts("Impossible");
85         else cout << res << endl;
86     }
87     return 0;
88 }