import sys
sys.setrecursionlimit(100000000)
MOD = 10 ** 9 + 7
INF = 10 ** 15
import numpy as np

def main():  
    N = int(input())
    A = np.array([input() for _ in range(N - 1)],np.int32)
    count = np.zeros(N,np.int32)
    bus = np.array([input().split() for _ in range(N)],np.int32)
    count -= bus[:,0]
    count += bus[:,1]
    count = np.cumsum(count)
    ans = np.dot(count[:-1],A)
    print(ans)
if __name__ == '__main__':
    main()