n = int(input())

a = [0]
b = [0]
c = [0]

num = 0
ans = 0 

for i in range(1,n):
    a.append(int(input()))

for i in range(1, n+1):
    b.append(int(input()))
    c.append(int(input()))

for i in range(1,n):
    num = num-b[i]+c[i]
    ans += a[i] * num

print(ans)