https://zerojudge.tw/ShowProblem?problemid=b966

oj.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# @Date    : 2019-02-16 08:59:40
# @Author  : Racter (vivi.450@hotmail.com)
# @Profile    : https://racterub.me

# OJ: https://zerojudge.tw/ShowProblem?problemid=b966

while 1:
    try:
        count = int(input().strip())
        data = [list(map(int, input().strip().split(' '))) for i in range(count)]
        data = sorted(data, key=lambda v:v[1]) # sorted with start value to prevent data needs to jump to different block back and forth
        s = data[0][0]
        e = data[0][1]
        length = e-s
        for i in data[1:]:
            if i[0] < e and i[1] > e:
                e = i[1]
            elif i[0] > e:
                length += (e-s)
                s = i[0]
                e = i[1]
        print(length)
    except EOFError:
        break