from sys import stdin

def main():
    N, M = [int(i) for i in input().split()]
    aru = {}
    for i in range(M):
        b, k = [int(i) for i in stdin.readline().split()]
        if b not in aru:
            aru[b] = 1
        else:
            aru[b] += 1
        if k not in aru:
            aru[k] = -1
        else:
            aru[k] -= 1
    ar = sorted([[a,aru[a]] for a in aru])
    ##print(ar)
    cs = 0
    dbar = len(ar)
    db = 0
    if ar[0][0] > 1:
        db = 1
    for i in range(dbar):
        cs += ar[i][1]
    ##    print(ar[i],cs)
        if cs == 0 and ar[i][1] < 0 and ar[i][0] < N:
            db += 1
    print(db)

main()