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