#include <stdio.h>
#include <stdlib.h>

int main()
{
 int num;
 int a,b,c,d;
 while(scanf("%d",&num)==1)
 {while(scanf("%d,%d,%d,%d",&a,&b,&c,&d)==4)
  {if((b-a)==(c-b)){printf("%d\n",d+(b-a));}
   else{printf("%d\n",d*(b/a));}
  }
 }
 return 0;
}

while( scanf( "%d %d %d %d", &a, &b, &c, &d ) == 4 )

另外,要輸出前五項