import strutils, sequtils, sugar

let
  n = parseInt stdin.readLine
  a = (n-1).newSeqWith parseInt stdin.readLine
  bcs = n.newSeqWith stdin.readLine.split.map parseInt
  xs = newSeq.collect:
    for bc in bcs:
      let
        b = bc[0]
        c = bc[1]
      c - b

var
  cnt = 0
  ans = 0

for i, v in a:
  cnt += xs[i]
  ans += v * cnt

echo ans