#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;



int main()
{
  ll Z,I,M,L,i,j,k,a,b,c,d,e,cas=1;
  while(cin>>Z>>I>>M>>L)
  {
      if(Z==0 &&I==0 &&L==0 &&M==0)
        break;
      ll cnt=0;
      c=(Z*L+I)%M;
      a=c;
      L=c;
      while(true)
      {
          cnt++;
          b=(Z*L+I)%M;
          if(b==a)
            break;
        L=b;
      }
      cout<<"Case "<<cas++<<": "<<cnt<<endl;
  }
  return 0;
}