n, C = map(int, input().split())
ab = [tuple(map(int, input().split())) for _ in range(n)]

total_individual = 0
min_all = float('inf')

for j in range(n):
    a_j, b_j = ab[j]
    pos = j + 1  # Convert to 1-based index
    left = pos - 1
    right = n - pos
    sum_left = left * (left + 1) // 2
    sum_right = right * (right + 1) // 2
    total_sum = sum_left + sum_right
    cost = b_j + n * a_j + C * total_sum
    if cost < min_all:
        min_all = cost
    total_individual += a_j + b_j

print(min(min_all, total_individual))