# coding: utf-8

n = int(input())
data = []
data_set = []
total = 0

for i in range(n):
    tmp = list(map(int, input().split()))
    data_set.append([min(tmp[0], tmp[2]), min(tmp[1], tmp[3]), max(tmp[0], tmp[2]),max(tmp[1], tmp[3])])
    total += (abs(tmp[0] - tmp[2]) + 1) * (abs(tmp[1] - tmp[3]) + 1)
    data.append(tmp)

for i in range(n - 1):
    ax1, ay1, ax2, ay2 = data_set[i]

    for j in range(i + 1, n):
        bx1, by1, bx2, by2 = data_set[j]
        x_len = max(0, min(ax2, bx2) - max(ax1, bx1) + 1)
        if x_len == 0:
            continue
        y_len = max(0, min(ay2, by2) - max(ay1, by1) + 1)
        if y_len == 0:
            continue
        total -= x_len * y_len
print(total)