1 #include<stdio.h>
 2 #include<algorithm>
 3 using namespace std;
 4 #define MAX(x,y) x>y?x:y
 5 #define MIN(x,y) x<y?x:y
 6 int judge(int x,int y){
 7     int a,b;
 8     a=MAX(x,y);
 9     b=MIN(x,y);
10     if((a-b)%3==0)return a;
11     else return 0;
12 }
13 int main(){
14     int Y,B,R,temp[3],flot;
15     while(~scanf("%d%d%d",&Y,&B,&R)){flot=1;
16     temp[0]=judge(Y,B),temp[1]=judge(Y,R),temp[2]=judge(B,R);
17         sort(temp,temp+3);
18         for(int i=0;i<3;i++){
19             if(temp[i]){flot=0;
20                 printf("%d\n",temp[i]);break;
21             }
22         }
23         if(flot)printf("):\n");
24     }
25     return 0;
26 }