# coding: utf-8


def main():
    n = int(input())
    al = [int(input()) for _ in range(n-1)]
    bl = [list(map(int, input().split(' '))) for _ in range(n)]
    ans = [al[i] * num(bl, i) for i in range(n-1)]
    print(sum(ans))


def num(bl, i):
    return sum([l[1] - l[0] for l in bl[:i+1]])


if __name__ == '__main__':
    main()