⎕io←0
 p←'#'=↑⊃⎕NGET'input'1
 f←{+/p[↓⍉↑(⍴p)|⍵×2⍴⊂⍳⌈(⊃⍴p)÷⊃⍵]}
 f 1 3  ⍝ Part 1
 ×/f¨(1 1)(1 3)(1 5)(1 7)(2 1)  ⍝ Part 2