N,K = map(int,input().split())
AB = []
inf = 10**100
for i in range(N):
    a,b = map(int,input().split())
    AB.append([a,b])
def check(x):
    count = 0
    for i in range(N):
        if A[i] <= x:
            count += min(B[i],x) -A[i] +1
    return K <= count

def main():
    ng = 0
    ok = inf
    while(ng + 1 != ok):
        mid = (ng+ok)/2
        if check(mid):
            ok = mid
        else:
            ng = mid
    print(ok)
main()