n,w = map(int,input().split())
pt = [tuple(map(int,input().split())) for i in range(n)]
lo = 0
hi = 1
def flour(totalt):
    ans=0
    for p,t in pt:
        left = totalt-t*2
        if left>0:
            ans+=left*p
    return ans

while flour(hi)<w:
    hi*=2
lo = hi//2
for i in range(64):
    mid = (lo+hi)/2
    if flour(mid)>=w:
        hi = mid
    else:
        lo = mid
print(lo)