Trace of a Matrix
Compute the trace, the sum of the main diagonal of a square grid.
Input format
The first line has two integers R and C (with R = C, a square matrix). Each of the next R lines has C space-separated integers describing one row.
Output format
Print the trace of the matrix: the sum of the elements on the main diagonal.
Constraints
- Values fit in a 64-bit signed integer
- Trailing whitespace and a trailing newline are ignored by the judge
Read from stdin, write to stdout. Sample cases below show the exact format.
Sample cases
Example 1
Input
2 2
5 1
1 5Expected output
10Example 2
Input
3 3
2 0 0
0 3 0
0 0 4Expected output
9