n = int(input())

a = []

result = 0

for i in range (n):

x, y = map(int, input().split())

a.append([x, y])

a.sort()

Head = a[0][0]

Tail = a[0][1]

for i in range (1, n):

# 新段

if (a[i][0] > Tail):

result += Tail - Head

Head = a[i][0]

Tail = a[i][1]

#更新線段

elif (Tail >= a[i][0] and a[i][1] > Tail):

Tail = a[i][1]

print(result + (Tail - Head))