There are n different online courses numbered from 1 to n. You are given an array courses where courses[i] = [durationi, lastDayi] indicate that the ith course should be taken continuously for durationi days and must be finished before or on lastDayi.
You will start on the 1st day and you cannot take two or more courses simultaneously.
Return the maximum number of courses that you can take.
\n\n\n
Example 1:
\n\n\nInput: courses = [[100,200],[200,1300],[1000,1250],[2000,3200]]\nOutput: 3\nExplanation: \nThere are totally 4 courses, but you can take 3 courses at most:\nFirst, take the 1st course, it costs 100 days so you will finish it on the 100th day, and ready to take the next course on the 101st day.\nSecond, take the 3rd course, it costs 1000 days so you will finish it on the 1100th day, and ready to take the next course on the 1101st day. \nThird, take the 2nd course, it costs 200 days so you will finish it on the 1300th day. \nThe 4th course cannot be taken now, since you will finish it on the 3300th day, which exceeds the closed date.\n\n\n
Example 2:
\n\n\nInput: courses = [[1,2]]\nOutput: 1\n\n\n
Example 3:
\n\n\nInput: courses = [[3,2],[4,3]]\nOutput: 0\n\n\n
\n
Constraints:
\n\n1 <= courses.length <= 1041 <= durationi, lastDayi <= 104这里有 n 门不同的在线课程，按从 1 到 n 编号。给你一个数组 courses ，其中 courses[i] = [durationi, lastDayi] 表示第 i 门课将会 持续 上 durationi 天课，并且必须在不晚于 lastDayi 的时候完成。
你的学期从第 1 天开始。且不能同时修读两门及两门以上的课程。
返回你最多可以修读的课程数目。
\n\n\n\n
示例 1：
\n\n\n输入：courses = [[100, 200], [200, 1300], [1000, 1250], [2000, 3200]]\n输出：3\n解释：\n这里一共有 4 门课程，但是你最多可以修 3 门：\n首先，修第 1 门课，耗费 100 天，在第 100 天完成，在第 101 天开始下门课。\n第二，修第 3 门课，耗费 1000 天，在第 1100 天完成，在第 1101 天开始下门课程。\n第三，修第 2 门课，耗时 200 天，在第 1300 天完成。\n第 4 门课现在不能修，因为将会在第 3300 天完成它，这已经超出了关闭日期。\n\n
示例 2：
\n\n\n输入：courses = [[1,2]]\n输出：1\n\n\n
示例 3：
\n\n\n输入：courses = [[3,2],[4,3]]\n输出：0\n\n\n
\n\n
提示:
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