def ceildiv(a: int, b: int) -> int:
    return (a + b - 1) // b


INF = 1 << 62
N, M = map(int, input().split())
xs = []
for _ in range(N):
    a, b = map(int, input().split())
    xs.append((a, b))

ys = sorted([ceildiv(M-a+1, b) for a, b in xs])

def can(m: int) -> bool:
    for d, i in enumerate(range(0, N, m), 1):
        for j in range(i, min(N, i+m)):
            if d > ys[j]:
                return False

    return True


lo = 1
hi = INF
ans = hi
while lo <= hi:
    m = (lo + hi) // 2
    if can(m):
        ans = min(ans, m)
        hi = m - 1
    else:
        lo = m + 1

print(ans)