import sys

sys.setrecursionlimit(10**6)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def FI(): return float(sys.stdin.buffer.readline())
def MI(): return map(int, sys.stdin.buffer.readline().split())
def MF(): return map(float, sys.stdin.buffer.readline().split())
def MI1(): return map(int1, sys.stdin.buffer.readline().split())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
inf = 10**16
# md = 998244353
# md = 10**9+7

n,k=MI()
cd=[]
for _ in range(n):
    a,b=MI()
    cd.append((a,1))
    cd.append((b+1,-1))
cd.sort()
now=0
s=0
pc=-1
for c,d in cd:
    # print(c,d,now,s)
    if s+now*(c-pc)>=k:
        ans=pc+(k-s-1)//now
        print(ans)
        exit()
    s+=now*(c-pc)
    pc=c
    now+=d