def main():

    n,m=list(map(int,input().split()))

    CARD=[0]*(n+1)

    for i in range(m):

        L,R=list(map(int,input().split()))

        CARD[L-1]+=1

        CARD[R]-=1

    ans=0

    for i in range(n):

        if CARD[i]==m:ans+=1

        CARD[i+1]=CARD[i+1]+CARD[i]



    print(ans)



if __name__=='__main__':

    main()
def main():

    import sys

    input = sys.stdin.readline



    n,m=list(map(int,input().split()))

    CARD=[0]*(n+1)

    for i in range(m):

        L,R=list(map(int,input().split()))

        CARD[L-1]+=1

        CARD[R]-=1

    ans=0

    for i in range(n):

        if CARD[i]==m:ans+=1

        CARD[i+1]=CARD[i+1]+CARD[i]



    print(ans)



if __name__=='__main__':

    main()

def main():
    n, m = list(map(int, input().split()))
    CARD = [0] * (n + 1)
    for i in range(m):
        L, R = list(map(int, input().split()))
        CARD[L - 1] += 1
        CARD[R] -= 1
    ans = 0
    for i in range(n):
        if CARD[i] == m:
            ans += 1
        CARD[i + 1] = CARD[i + 1] + CARD[i]
    print(ans)


if __name__ == "__main__":
    main()

def main():
    import sys

    input = sys.stdin.readline
    n, m = list(map(int, input().split()))
    CARD = [0] * (n + 1)
    for i in range(m):
        L, R = list(map(int, input().split()))
        CARD[L - 1] += 1
        CARD[R] -= 1
    ans = 0
    for i in range(n):
        if CARD[i] == m:
            ans += 1
        CARD[i + 1] = CARD[i + 1] + CARD[i]
    print(ans)


if __name__ == "__main__":
    main()

+    import sys + +    input = sys.stdin.readline