#include <iostream>
#include <math.h>
#include <vector>
#include <unordered_map>

using namespace std;
int minSteps;
vector<int> getPrimes(int a) {
    vector<int> vec;
    for (int i = 2; a > 1; ++i)  {
        while (a % i == 0) {
            if (vec.empty() || vec.back() != i) {
                vec.push_back(i);
            }
            a /= i;
        }
    }
    return vec;
    //m[a] = vec;
}

//unordered_map <int,vector<int>> m;

void addX (int A, int B, int steps) {
        //cout << A << " " << B << " " << steps << endl;
        vector<int> vec;
        if (A == B && steps < minSteps) {
            minSteps = steps;
            return;
        }
        if (A > B) {
            return;
        }
        if (A < 2) {
            return;
        }
        //if(m.find(A) ==  unordered_map::end){
            vec = getPrimes(A);
        //}
        // vector<int> vec = getPrimes(A);
        ++steps;
        for (int i = 0; i < vec.size(); ++i) {
            //addX(A + m[A][i], B, steps);
            addX(A + vec[i], B, steps);
        }
    }
int main() {
    int A, B;
    cin >> A >> B;
    int count = 0, steps;
    while (A != 0 || B != 0) {
        minSteps = 1000;
        count++;
        steps = 0;
        addX (A, B, 0);
        if (minSteps == 1000) {
            minSteps = -1;
        }
        cout << "Case " << count << ": " << minSteps << endl;
        cin >> A >> B;
    }
}