import sequtils,strutils
var
    n = stdin.readline.parseInt
    A = newSeq[int](0)
    b,c,B,ans : int

for i in 1..<n:
    A.add(stdin.readline.parseInt)
for i in 0..<n:
    (b, c) = stdin.readline.split.map(parseInt)
    B -= b
    B += c
    if i != n - 1:
        ans += A[i] * B
    
echo ans