from sys import stdin
input = stdin.readline
from collections import defaultdict

INF = 1<<60

N, X = map(int, input().split())
AB = [list(map(int, input().split())) for _ in range(N)]

if X == 1:
    exit(print(max(b for _, b in AB)))

D = defaultdict(int)
for A, B in AB:
    D[B//X] += A
D = sorted(D.items(), key=lambda x:x[0], reverse=True)
costD = 0
SUM = 0
for n, c in D:
    SUM += c
    if X < SUM:
        costD = n
        break

ans2 = INF
for cost in range(costD-5, costD+6):
    if cost < 0: continue
    SUM = 0
    AB2 = []
    for i in range(N):
        A, B = AB[i]
        n = B//X
        if cost < n:
            SUM += A*(n-cost)
            B -= X*(n-cost)
        AB2.append([A, B])

    AB2.sort(key=lambda x:x[1], reverse=True)
    AB2.append([0, 0])
    ans = SUM+AB2[0][1]
    MAX = -1
    for i, (A, B) in enumerate(AB2[:-1]):
        if B//X < cost:
            break
        SUM += A
        MAX = max(MAX, B-X)
        ans = min(ans, SUM+max(AB2[i+1][1], MAX))
    ans2 = min(ans2, ans)

print(ans2)