a = list(input().split())
b = []
c = int(a[0])+1
d = []
for i in range(int(a[1])):
    b.append(input().split())
for x in range(1,c):
    for y in b:
        if(x >= int(y[0]) and x <= int(y[1])):
            if(x not in d):
                c -= 1
                d.append(int(x))
print(str(c))

我感觉运行得挺快的啊！