UVa 11730 - Number Transformation

/*
Lionel Messi is such a player that you may catch him, you may touch him, you may feel him
and definitely you may Love him.
Lionel Messi is Messi. A little Magician in this World.

*/

// Accepted

#include<bits/stdc++.h>

using namespace std;

#define fast ios_base::sync_with_stdio(0)
#define bfast cin.tie(0)
#define outs(x) cout << x << " "
#define outn(x) cout << x << "\n"
#define sf scanf
#define pf printf
#define nl puts("")
#define psb push_back
#define mset(c,v) memset(c , v , sizeof c)
#define loop0(n) for(int i=0; i<n; i++)
#define loop1(n) for(int i=1; i<=n; i++)
#define mpair(x , y) make_pair(x , y)
#define all(x) x.begin(), x.end()
#define pi acos(-1.0)
#define psb push_back

typedef unsigned long long ull;
typedef long long LL;
typedef vector<int>vii;
typedef vector<LL>vll;
typedef vector<string>vs;
typedef map<int, int>mpii;
typedef map<string, int>mpsi;
typedef map<char, int>mpci;
typedef map<LL, LL>mpll;

const int mod = 1000007;
const int high = 1002;
const int qrt = 32;

bool mark[high] , visited[high];
int prm[high] , plen=0 , cost[high] , S , T;

void sieve()
{
    int i , j;

    mset(mark, false);

    for(i=3; i<qrt; i+=2)
    {
        if(!mark[i])
        {
            for(j=i*i; j<high; j+=(2*i))
            {
                mark[j] = true;
            }
        }
    }

    prm[plen++] = 2;

    for(i=3; i<high; i+=2)
    {
        if(!mark[i])
        {
            prm[plen++] = i;
        }
    }

    //for(i=0; i<100; i++) cout << prm[i] << "; ";
}


int BFS(int s)
{
     mset(visited, false);
     mset(cost , 0);

    int A , x , sum=0;

    visited[s] = true;

    cost[s] = 0;

    if(s == T) return 0;

    queue<int>Q;

    Q.push(s);

    while(!Q.empty())
    {
        A = Q.front();

        Q.pop();

        for(int i=0; i<plen && prm[i] < A; i++)
        {
            x = prm[i];

            if(!(A % x))
            {
                sum = A + x;

                if(sum == T) return cost[A] + 1;

                if(!visited[sum] && sum <= T)
                {
                    visited[sum] = true;
                    cost[sum] = cost[A] + 1;
                    Q.push(sum);
                }
            }
        }
    }

    return -1;
}

int main()
{
    //freopen("out.txt", "w" , stdout);
    fast;
    sieve();

    int tc = 0;

    while(cin >> S >> T)
    {
        if(!S && !T) break;

        int ans = BFS(S);

        cout << "Case " << ++tc << ": ";

        outn(ans);
    }

    return 0;
}