lis = list(input().split())
len = int(lis[0])
a = int(lis[1])
i = 0
l = [0] * len
u = v = 0
count = len + 1
import sys
while(i < a):
    u , v = map(int , input().split())
    if(u > v):
        sys.exit()
    while(u <= v):
        if(l[u] == 0):
            l[u] = 1
            count -= 1
        u += 1
    i += 1
print(count)