import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)
##############################

N = int(input())
A = []
for i in range(N-1):
    a = int(input())
    A.append(a)

B = []
C = []
for i in range(N):
    b, c = map(int, input().split())
    B.append(b)
    C.append(c)

t = []
for i in range(N):
    diff = C[i]-B[i]
    t.append(diff)


for i in range(1, N):
    t[i] += t[i-1]

#print(t)
ans = 0
for i in range(N-1):
    ans += t[i]*A[i]

print(ans)