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Candies
Description During
the kindergarten days, flymouse was the monitor of his class.
Occasionally the head-teacher brought the kids of flymouse¡¯s class a
large bag of candies and had flymouse distribute them. All the kids
loved candies very much and often compared the numbers of candies they
got with others. A kid A could had the idea that though it might be the
case that another kid B was better than him in some aspect and
therefore had a reason for deserving more candies than he did, he
should never get a certain number of candies fewer than B did no matter
how many candies he actually got, otherwise he would feel dissatisfied
and go to the head-teacher to complain about flymouse¡¯s biased
distribution. snoopy shared class with flymouse at that time.
flymouse always compared the number of his candies with that of
snoopy¡¯s. He wanted to make the difference between the numbers as large
as possible while keeping every kid satisfied. Now he had just got
another bag of candies from the head-teacher, what was the largest
difference he could make out of it? Input The input contains a single test cases. The test cases starts with a line with two integers N and M not exceeding 30 000 and 150 000 respectively. N is the number of kids in the class and the kids were numbered 1 through N. snoopy and flymouse were always numbered 1 and N. Then follow M lines each holding three integers A, B and c in order, meaning that kid A believed that kid B should never get over c candies more than he did. Output Output one line with only the largest difference desired. The difference is guaranteed to be finite. Sample Input Sample Output Hint Source |
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