N,K = map(int, input().split())
AB  = [list(map(int, input().split())) for _ in range(N)]

ok = 10**9
ng = 0
mid = (ok+ng)//2
while abs(ok-ng) > 1:
    tmpCount = 0
    for a,b in AB:
        n = b-a+1
        if b < mid:
            tmpCount += n
        elif mid < a:
            pass
        elif a <= mid <= b:
            tmpCount += mid - a + 1
        
    if tmpCount >= K:
        ok = mid
    else:
        ng = mid
    mid = (ok+ng)//2
print(ok)