import 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
  acc = xs.foldl(a + max.pred b, 0)

echo:
  if (acc mod 2) == 0: acc div 2
  else: -1