import math, sequtils, strscans, sugar

let
  input = stdin.lines.toseq
  xs = newSeq.collect:
    for i, str in input:
      if i == 0: continue
      let
        (_, a, b) = str.scanTuple"$i $i"
      a + b * 4
  max = max xs
  xs2 = xs.mapIt(max.pred it)
  sum = xs2.sum

echo:
  if xs2.allIt (it mod 2) == 0: sum div 2
  else: -1