素数路

#include <iostream>
#include <string>
#include <algorithm>
#include <cstring>
#include <queue>
#include <cstdio>
using namespace std;
typedef pair<int, int>P;
int a[3000], n = 0, x, y;

int ok(int n, int m){
    int cnt = 0;
    while(n > 0){
        if(n%10 == m%10) cnt++;
        n /= 10;
        m /= 10;
    }
    return cnt;
}
void init(){
      for(int i = 1000; i <= 10000; i++){
        int flag = 1;
        for(int j = 2; j*j <= i; j++){
            if(i % j == 0){
                flag = 0;
                break;
            }
        }
        if(flag){
            a[n++] = i;
        }
    }
}
int bfs(){
    int vis[10003];
    memset(vis, 0, sizeof(vis));
    queue<P>s;
    s.push(P(x, 0));
    vis[x] = 1;
    while(!s.empty()){
        P p = s.front();
        s.pop();
        if(y == p.first){
            return p.second;
        }
        for(int i = 0; i < n; i++){
            if(vis[a[i]] == 0 && ok(p.first, a[i]) == 3){
               // printf("%d\n", a[i]);
                vis[a[i]] = 1;
                s.push(P(a[i], p.second+1));

            }
        }
    }
    return -1;
}
int main()
{
    init();
    cin >> x >> y;
    int ans = bfs();
    if(ans == -1){
        printf("Impossible\n");
    }else printf("%d\n", ans);

    return 0;
}