1373: C++二级辅导-对角线和
          Memory Limit:128 MB
          Time Limit:1.000 S
         
      
      
        
          Judge Style:Text Compare
          Creator:
      
      
          Submit:15
          Solved:15
      
Description
求一个3×3矩阵对角线元素之和。
Sample Input Copy
1 2 3
4 5 6
7 8 9
Sample Output Copy
15