import sys
from itertools import accumulate

def main():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    acc = [0] * (N+1)
    for _ in range(M):
        left, right = map(int, input().split())
        acc[left-1] += 1
        acc[right] -= 1

    cnt = 0
    for a in accumulate(acc):
        if a == M:
            cnt += 1

    return cnt


if __name__ == '__main__':
    print(main()) import sys sys from itertools import accumulate def main():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    acc = [0] * (N+1)
    for _ in range(M):
        left, right = map(int, input().split())
        acc[left-1] += 1
        acc[right] -= 1

    cnt = 0
    for a in accumulate(acc):
        if a == M:
            cnt += 1

    return cnt main input = sys.stdin.readline input sys.stdin.readline sys.stdin sys stdin readline N, M = map(int, input().split()) N map(int, input().split()) map int input().split() ().split () input split M acc = [0] * (N+1) acc [0] * (N+1) [0] 0 N+1 N 1 for _ in range(M):
        left, right = map(int, input().split())
        acc[left-1] += 1
        acc[right] -= 1

     _ range(M) range M left, right = map(int, input().split()) left map(int, input().split()) map int input().split() ().split () input split right acc[left-1] += 1 acc[left-1] acc left-1 left 1 1 acc[right] -= 1 acc[right] acc right 1 cnt = 0 cnt 0 for a in accumulate(acc):
        if a == M:
            cnt += 1

     a accumulate(acc) accumulate acc if a == M:
            cnt += 1

     a == M a M cnt += 1 cnt 1 return cnt cnt if __name__ == '__main__':
    print(main()) __name__ == '__main__' __name__ '__main__' print(main()) print main() main def main():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    acc = [0] * (N+1)
    for _ in range(M):
        left, right = map(int, input().split())
        acc[left-1] += 1
        acc[right] -= 1

    cnt = 0
    for a in accumulate(acc):
        if a == M:
            cnt += 1

    return cnt def main():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    acc = [0] * (N+1)
    for _ in range(M):
        left, right = map(int, input().split())
        acc[left-1] += 1
        acc[right] -= 1

    cnt = 0
    for a in accumulate(acc):
        if a == M:
            cnt += 1

    return cnt main
import sys
from itertools import accumulate

def main():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    acc = [0] * (N+1)
    for _ in range(M):
        left, right = map(int, input().split())
        acc[left-1] += 1
        acc[right] -= 1

    cnt = 0
    for a in accumulate(acc):
        if a == M:
            cnt += 1

    return cnt


if __name__ == '__main__':
    print(main())