As Soon As Possible

import collections

​

N, M = map(int, input().split())

ABST = [list(map(int, input().split())) for i in range(M)]

ABST = sorted(ABST, key=lambda x: x[2])

d = collections.defaultdict(lambda: float('inf'))

​

d[1]=0

for a,b,s,t in ABST:

    if d[a]<=s:

        d[b] = min(d[b],t)

if d[N]==float('inf'):

    print(-1)

else:

    print(d[N])