Time limit 1000/1000/1000/1000 ms. Memory limit 65000/65000/65000/65000 Kb.
Problem description
A train leaves the first station with N passengers and visits K stations before
it arrives at the last station. In each station some passengers got off the train
and some passengers got on the train. Everybody in the train got off at the last
station. Make a program that calculates how many passengers got off the train
at the last station.
Input
The first line of the input has two integers N and K. Each of the following K lines
contains two integers, the first one denotes the number of passengers who got
off the train at that station, and the second one denotes the number of
passengers got on the train at that station.
Output
The output should hava a single
integer that is number of passengers who got off the train at the last station.
Example
| stdin |
stdout |
5 20
6 15
5 30
20 12
15 8
6 7 |
40 |
Для отправки решений необходимо выполнить вход.
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