N,K = map(int,input().split())

edge = []
for _ in range(N):
    a,b = map(int,input().split())
    edge.append((a,b))
    
def check(x):
    count = 0
    for a,b in edge:
        if a <= x <= b:
            count += x - a + 1
        elif x > b:
            count += b - a + 1
    return count >= K
start = 0
end = 10 ** 9
while end - start > 1:
    mid = (end + start) // 2
    if check(mid):
        end = mid
    else:
        start = mid
print(end)