hdu 1229

#include<stdio.h>

#include<iostream>

using namespace std;

bool Judge(int num1,int num2,int k)

{

if(k == 0)

return false;

for(int i=1;i<=k;i++)

{

if((num1%10) != (num2%10))

return false;

num1/=10;

num2/=10;

}

return true;

}

int main()

{

int num1,num2,k;

while(scanf("%d %d %d",&num1,&num2,&k),num1,num2)

{

if(Judge(num1,num2,k))

printf("-1\n");

else

printf("%d\n",num1+num2);

}

return 0;

}