n=int(input())
yen=[]
cnt=0
fee=0
h=[[] for i in range(2)]
for i in range(n-1):
    yen.append(int(input()))
for i in range(n):
    a=list(map(int,(input().split())))
    h[0].append(a[0])
    h[1].append(a[1])
for i in range(n-1):
    cnt+=(-h[0][i]+h[1][i])
    fee+=(cnt*yen[i])
print(fee)