# -*- coding:utf-8 -*-

columnCuount = int(input())
barCount = int(input())

barMap = []

for i in range(barCount):
    barMap.append([int(j) - 1 for j in input().rstrip().split(" ")])

numList = [[i, i] for i in range(columnCuount)]


def getGoal(column):
    current = column
    for (f, t) in barMap:
        if t == current:
            current = f
        elif f == current:
            current = t
    return current


moveList = [getGoal(i) for i in range(columnCuount)]

for i in range(1000000):
    tmp = sorted([[moveList[i], v] for (i, v) in numList])
    if len([[i,v] for (i,v) in tmp if i != v]) == 0:
        print(str(i+1))
        exit(0)
    numList = tmp