学步园

#include <iostream>
using namespace std;
char a[11];
int  main()
{
	while(cin >> a)
	{
		int sum = 0; 
		int index = 0;
		int i;
		for(i = 0; i < 10; i++)
		{
			if(a[i] == '?')
				index = i;
			else if(a[i] == 'X')
				sum += (10-i) * 10;
			else
				sum += (10-i) * (a[i] - '0');
		}
		for(i =0; i <= 10; i++)
		{
			if((sum + i *(10 - index))%11 == 0 )
				break;
		}
		if(i == 10)
		{
			if(index != 9)
				cout << "-1" << endl;
			else
				cout << "X" << endl;
		}
		else
			cout << i  << endl;
	}
	return 0;
}