学步园

简单题，但是WA了很多次。。

#include  <iostream>
using namespace std;

int main()
{
	int a, b, k;
	while(cin >> a >> b >> k, a || b)
	{
		if(a == b)
		{
			cout << "-1" << endl;
			continue;
		}
		if(k >=5)
		{
			cout << a + b << endl;
			continue;
		}
		char str1[10], str2[10];
		int x = a;
		int y = b;
		x += 10000;
		y += 10000;
		itoa(x, str1, 10);
		itoa(y, str2, 10);
		int flag = 0;
		for(int i = 0; i < k; i++)
		{
			if(str1[4-i] != str2[4-i])
			{
				flag = 1;
				break;
			}
		}
		if(flag == 1)
			cout << a + b << endl;
		else
			cout << "-1" << endl;
	}
	return 0;
}