用k*k的方格覆蓋單元格（i，j）,單元格可以被覆蓋幾次？

https://codeforces.com/contest/2000/problem/E
\((min(i-1,n-k) - max(-1,i-1-k))*(min(j-1,m-k)-max(-1,j-1-k))\)
\(1<=i<=n\) && \(1<=j<=m\)