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.
输入描述:
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.
输出描述:
Print a single integer — the minimum amount of time in seconds needed to bring all the passengers to floor 0.
示例1
输入
3 7<br />2 1<br />3 8<br />5 2<br />5 10<br />2 77<br />3 33<br />8 21<br />9 12<br />10 64<br />
备注:
In the first sample, it takes at least 11 seconds to bring all passengers to floor 0. Here is how this could be done:1. Move to floor 5: takes 2 seconds.2. Pick up passenger 3.3. Move to floor 3: takes 2 seconds.4. Wait for passenger 2 to arrive: takes 4 seconds.5. Pick up passenger 2.6. Go to floor 2: takes 1 second.7. Pick up passenger 1.8. Go to floor 0: takes 2 seconds.This gives a total of 2 + 2 + 4 + 1 + 2 = 11 seconds.
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