#include <iostream>

 #include <cstring>

 #include <cstdio>

 #include <algorithm>

 using namespace std;

 const int Maxn=;

 int f[Maxn],n,Ans;

 int Gcd(int a,int b) {if (b==) return a; return Gcd(b,a%b);}

 inline int Abs(int x) {return x>?x:-x;}

 int main()

 {

     while (true)

     {

         n=;

         scanf("%d",&f[++n]);

         if (f[n]==) break;

         while (f[n]!=) scanf("%d",&f[++n]);

         n--;

         for (int i=;i<n;i++)

             f[i]=f[i]-f[i+];

         Ans=f[];

         for (int i=;i<n;i++)

             Ans=Gcd(f[i]==?Ans:f[i],Ans);

         printf("%d\n",Abs(Ans));

     }

     return ;

 }