INF = 10 ** 9
MOD = 10 ** 9 + 7
import sys
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)
from  math import factorial

def f(x,C):
        S = 0
        t = 0
        for a,b in C:
            if x < a:
                continue
            if b < x:
                S += b - a + 1
            elif a <= x <= b:
                S += x - a
                t += 1
        return  S,t

def main():
    n,k = map(int,input().split())
    C = [tuple(map(int,input().split())) for _ in range(n)]

    l = 0
    r = 10 ** 9 + 1
    while r - l > 1:
        mid = (r + l)//2
        S,t = f(mid,C)
        if S < k <= S + t:
            break
        if S >= k:
            r = mid
        else:
            l = mid 
    print(mid)
if __name__ == '__main__':
    main()