题挺简单的，就是看细心不细心，考虑的全不全，我就是少考虑个条件，一直错，必须记下来
Today an outstanding event is going to happen in the forest — hedgehog Filya will come to his old fried Sonya!
Sonya is an owl and she sleeps during the day and stay awake from minute l1 to minute r1 inclusive. Also, during the minute k she prinks and is unavailable for Filya.
Filya works a lot and he plans to visit Sonya from minute l2 to minute r2 inclusive.
Calculate the number of minutes they will be able to spend together.
Input
The only line of the input contains integers l1, r1, l2, r2 and k (1 ≤ l1, r1, l2, r2, k ≤ 1018, l1 ≤ r1, l2 ≤ r2), providing the segments of time for Sonya and Filya and the moment of time when Sonya prinks.
Output
Print one integer — the number of minutes Sonya and Filya will be able to spend together.
Sample Input
Input
1 10 9 20 1
Output
2
Input
1 100 50 200 75
Output
50
Hint
In the first sample, they will be together during minutes 9 and 10.
In the second sample, they will be together from minute 50 to minute 74 and from minute 76 to minute 100.
(r2>=l1自己没考虑）
代码：
#include <iostream>
#include<stdio.h>
#include<algorithm>
#include<stdlib.h>
#include<string.h>
using namespace std;
#define maxn 100010
int main()
{
unsigned long long int s,m,n,k,l1,r1,l2,r2;
while(scanf("%lld%lld%lld%lld%lld",&l1,&r1,&l2,&r2,&k)!=EOF)
{
m=max(l1,l2);
n=min(r1,r2);
s=0;
if(l2<=r1&&r2>=l1)
{
s=n-m+1;
if(k>=m&&k<=n)
s--;
}
printf("%lld\n",s);
}
return 0;
}