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28 lines
647 B
28 lines
647 B
import functools
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a,b =map(int, input().split(' '))
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nums=[]
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for i in range(b):
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m,n=map(int,input().split(' '))
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if m>n:continue;
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nums.append([m,n])
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def cmp(a,b):#升序
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if(a[0]>b[0]):
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return 1
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else :
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return -1#不变
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nums=sorted(nums,key=functools.cmp_to_key(cmp))
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# for i in nums:
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# print(i)
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sum = 0
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start,end=nums[0][0],nums[0][1]
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count=1
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while count<len(nums):
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if nums[count][0]>=start and nums[count][0]<=end:
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if end<=nums[count][1]:
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end=nums[count][1]
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else :
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sum+=end-start+1
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start=nums[count][0];end=nums[count][1]
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count+=1
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sum+=end-start+1
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print(a-sum+1) |