def cond(arr,m):
    ret=0
    for v1,v2 in arr:
        if v1<=m<=v2:
            ret+=(m-v1+1)
        elif v2<m:
            ret+=(v2-v1+1)
    return ret

n,k=map(int,input().split())
arr=[list(map(int,input().split())) for _ in range(n)]
l=0
r=10**9+1
while r-l!=1:
    m=(r+l)//2
    if cond(arr,m)>=k:
        r=m
    else:
        l=m
print(r)