A. Saitama Destroys Hotel
题目连接：
http://www.codeforces.com/contest/608/problem/A
Description
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 fi and ti (1 ≤ fi ≤ s, 1 ≤ ti ≤ 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.
Sample Input
3 7
2 1
3 8
5 2
Sample Output
11
Hint
题意
有一个电梯，一开始停靠在第s层，这个电梯很奇怪，只能往下走
有n个人，他们会在第t秒出现在第f层
电梯每下一层需要1s，问你把这些人全部送到0层，最少需要多少秒
题解：
暴力扫一遍就好了，暴力扫每一层，这个电梯最少多少秒到达这一层就好了
每一层到达的时间，由上一层决定
有点像dp
代码
#include<bits/stdc++.h>
using namespace std;
#define maxn 1005
int a[maxn];
int main()
{
int n,s;scanf("%d%d",&n,&s);
for(int i=1;i<=n;i++)
{
int x,t;scanf("%d%d",&x,&t);
a[x]=max(t,a[x]);
}
int x,y;
int ans=0;
for(int i=s;i>=0;i--)
{
ans = max(ans,a[i]);
ans++;
}
cout<<ans-1<<endl;
}