397A-On Segment's Own Points

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探讨如何计算在限定条件下，Alexey能在多长的公共衣架上独占使用，避免衣物与其他学生接触。通过使用数组标记占用状态，实现简单有效的解决方案。

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Our old friend Alexey has finally entered the University of City N — the Berland capital. Alexey expected his father to get him a place to live in but his father said it was high time for Alexey to practice some financial independence. So, Alexey is living in a dorm.

The dorm has exactly one straight dryer — a 100 centimeter long rope to hang clothes on. The dryer has got a coordinate system installed: the leftmost end of the dryer has coordinate 0, and the opposite end has coordinate 100. Overall, the university has nstudents. Dean's office allows i-th student to use the segment (li, ri) of the dryer. However, the dean's office actions are contradictory and now one part of the dryer can belong to multiple students!

Alexey don't like when someone touch his clothes. That's why he want make it impossible to someone clothes touch his ones. So Alexey wonders: what is the total length of the parts of the dryer that he may use in a such way that clothes of the others (n - 1) students aren't drying there. Help him! Note that Alexey, as the most respected student, has number 1.

Input

The first line contains a positive integer n (1 ≤ n ≤ 100). The (i + 1)-th line contains integers li and ri (0 ≤ li < ri ≤ 100) — the endpoints of the corresponding segment for the i-th student.

Output

On a single line print a single number k, equal to the sum of lengths of the parts of the dryer which are inside Alexey's segment and are outside all other segments.

Sample test(s)

input
3
0 5
2 8
1 6

output
1

input
3
0 10
1 5
7 15

output
3

Note

Note that it's not important are clothes drying on the touching segments (e.g. (0, 1) and (1, 2)) considered to be touching or not because you need to find the length of segments.

In the first test sample Alexey may use the only segment (0, 1). In such case his clothes will not touch clothes on the segments (1, 6)and (2, 8). The length of segment (0, 1) is 1.

In the second test sample Alexey may dry his clothes on segments (0, 1) and (5, 7). Overall length of these segments is 3.

题意:Alexey有自己的一段衣架,并且不喜欢和别人分享..求他能单独挂衣服的长度是多少..

数组的第一行就是A的衣架长度...

一开始的时候,想到了很多限制条件,甚至分讨类论了!!!但是发现情况越分越多...于是在比赛的时候写不出来..

后来看了别人的做法..好奇妙...Get it~衣架的长度总共才100,所以可以用一个数组来表示此地是否被占领...

#include<stdio.h>
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
    int a[105],n,x,y,x0,y0;
    scanf("%d",&n);
    memset(a,0,sizeof(a));
    scanf("%d%d",&x0,&y0);
    for(int i=x0;i<y0;i++)
        a[i]=1;
    for(int i=1;i<n;i++)
    {
        scanf("%d%d",&x,&y);
        for(int i=x;i<y;i++)
            a[i]=0;
    }
    int s=0;
    for(int i=x0;i<y0;i++)
    {
        if(a[i])s++;
    }
    printf("%d\n",s);
    return 0;
}