hdu-1229

#include<stdio.h>int main(){int a,b,k;while(scanf("%d%d%d",&a,&b,&k)){if(a==0 && b==0)break;int n=1;for(int i=1;i<=k;++i)n=n*10;if(a%n == b%n)printf("-1\n");elseprintf("%d\n",a+b);}return 0;}