//Problem Practice C - Sequence

#include <iostream.h>

\\convert int A to base bb
int convert(int A, int bb)
{
	int n,b;
	b=bb;
	n = A%10;
	A = A/10;
	while(A>0)
	{
		n += (A%10)*b;
		b *= bb;
		A = A/10;
	}
	return n;
}

//find the starting base (find largest digit present,
// the startubg base is largest digit + 1)
int firstbase(int * nums, int n)
{
	//find largest digit
	int big=1,A,i;
	for(i=0;i<n;i++)
	{
		A=nums[i];
		while(A>0){
			if(A%10 > big)
				big = A%10;
			A=A/10;
		}
	}
	return big+1;
}

void main()
{
	int nums[5], diff, base, i,n,OK,start;

	cin>>n;
	while(n>0)
	{
		for(i=0;i<n;i++)
			cin>>nums[i];
		start=firstbase(nums,n);	//find starting base
		for(base=start;base<11;base++)
		{
			OK=1; //OK =1 until we find it's not arithmetic
			//get 1st difference
			diff = convert(nums[1],base)-convert(nums[0],base);
			//now check the other differences
			for(i=2;i<n;i++)
				if((convert(nums[i],base)-convert(nums[i-1],base)) != diff)
					OK=0;
				
			if (OK){
				cout<<"Minimum base = "<<base<<'.'<<endl;
				break;
			}
		}
		if (OK==0)
			cout<<"No base <= 10 can be found."<<endl;

		cin>>n;
	}
}