C :

int main (void)
{
	int a, b, k;
	int l; //除数

	while (1)
	{
		/*处理一行*/
		a = b = k = 0;
		l = 1;
		scanf("%d%d%d", &a, &b, &k);

		for (;k > 0; --k) 
		{
			l *= 10; 
		}

		if (a == 0 && b == 0)break;

		if ( a % l == b % l )
			printf("-1\n");
		else
			printf("%d\n", a+b);

	}

	return 0;
}

C++ :

#include<stdio.h>
#include<math.h>

int main()
{
	int a,b,k,i,m,t;
	while(scanf("%d%d%d",&a,&b,&k)!=EOF,a||b)
	{
		if(a==b)
			printf("-1\n");
		else
		{
			m=fabs(a-b);
			t=0;
			i=10;
			while(1)
			{
				if(m%i==0)
					t++;
				else
					break;
				i*=10;
			}
			printf(t>=k?"-1\n":"%d\n",a+b);
		}
	}
	return 0;
}

Java :

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		while(sc.hasNext()){
			int A=sc.nextInt(),B=sc.nextInt(),K=sc.nextInt();
			if(A==0&&B==0){
				break;
			}
			int n=1;
			while(K-->0){
				n*=10;
			}
			int output=A%n==B%n ? -1:A+B;
			System.out.println(output);
		}
		sc.close();
	}
}

Python :

while True:
    a, b, c = [int(i) for i in raw_input().split()]
    if b == 0 and a == 0:
        break
    if abs(a - b) % (10 ** c) == 0:
        print(-1)
    else:
        print(a + b)