def check(x): #x円以下あつめてk枚未満か？
    r = 0
    for a,b in ab:
        if a <= x <= b:
            r += x-a+1
        elif x > b:
            r += b-a+1
    return r < k


n,k = map(int,input().split())
ab = [list(map(int,input().split())) for _ in range(n)]

ok = 0
ng = 10**9+1
while ng-ok > 1:
    mid = (ok+ng)//2
    if check(mid):
        ok = mid
    else:
        ng = mid
print(ng)