Saitama Destroys Hotel CodeForces - 608A

Saitama accidentally destroyed a hotel again. To repay the hotel company, Genos has volunteered to operate an elevator in one of its other hotels. The elevator is special — it starts on the top floor, can only move down, and has infinite capacity. Floors are numbered from 0 to s and elevator initially starts on floor s at time 0.

The elevator takes exactly 1 second to move down exactly 1 floor and negligible time to pick up passengers. Genos is given a list detailing when and on which floor passengers arrive. Please determine how long in seconds it will take Genos to bring all passengers to floor 0.

Input

The first line of input contains two integers n and s (1 ≤ n ≤ 100, 1 ≤ s ≤ 1000) — the number of passengers and the number of the top floor respectively.

The next n lines each contain two space-separated integers f_i and t_i (1 ≤ f_i ≤ s, 1 ≤ t_i ≤ 1000) — the floor and the time of arrival in seconds for the passenger number i.

Output

Print a single integer — the minimum amount of time in seconds needed to bring all the passengers to floor 0.

Example

Input

3 72 13 85 2

Output

11

Input

5 102 773 338 219 1210 64

Output

79

题目大意：

 从最顶楼出发，下一楼花费一秒，如果到达某一层楼时总花费时间小于乘客所达到的时间则需要等待，求接到所有乘客的时间。

思路：

一开始没有考虑到一层楼的乘客可能分两批上，也就是一层楼的可能有两组数据，一直wa，后面问了学长才知道。这题的正确解法是:从顶楼到每一层楼的时间与这一层楼的乘客到达时间去比较，取大的那一个，也就是说每一组数据有一个标准值，我假设变量s为我们要求的值，把s与每一个标准值去比较即可。

第一次错的代码，就是没有考虑到同一层有两批人的

#include<cstdio>
#include<algorithm>
#include<string.h>
using namespace std;
int a[1005],s,n;
int main()
{
    while(scanf("%d%d",&n,&s)==2&&n&&s)
    {
        int x,y;
        memset(a,0,sizeof(a));
        for(int i=0;i<n;i++)
        {
            scanf("%d%d",&x,&y);
            a[x]=y;
        }
        int sum=0;
        for(int i=s;i>=0;i--)
        {
            if(a[i])
            {
                sum+=s-i;
                if(sum<a[i])
                    sum=a[i];
                s=i;
            }
        }
        printf("%d\n",sum+s);
    }
    return 0;
}

ac代码：

#include<cstdio>
#include<algorithm>
using namespace std;
int main()
{
    int n,s,sum;
    while(~scanf("%d%d",&n,&s))
    {
        sum=s;
        int x,y;
        for(int i=0;i<n;i++){
        scanf("%d%d",&x,&y);
        sum=max(x+y,sum);}
        printf("%d\n",sum);
    }
    return 0;
}