如题

#4，#7，#8 RE

或者帮忙下个数据点？（不知道为啥实名不了

a,n=map(int,input().split())
t=[[0,a]]
for i in range(n):
    x,y=map(int,input().split())
    for i in range(len(t)):
        p,q=t[i]
        if p<x<y<q:
            t[i]=[p,x-1]
            t.append([y+1,q])
        elif p<x<=q<=y:
            t[i]=[p,x-1]
        elif x<=p<=y<q:
            t[i]=[y+1,q]
        elif x<=p<q<=y:
            t.remove(t[i])
s=0
for i in t:
    s+=i[1]-i[0]+1
print(s)