from collections import deque

N, S = map(int, input().split())

St = [0] * N
Sc = [0] * N
for i in range(N):
    St[i], Sc[i] = map(int, input().split())
for i in range(1, N):
    St[i], Sc[i] = St[i] + St[i-1], Sc[i] + Sc[i-1]


# 凸包的下边界
que = deque()

# 因为Sc(-1) = 0, dp(-1) = 0, 一开始凸包里面就有这么一个初始点
que.append((-1, 0, -0x7fffffff)) # 三元组结构(下标i, dp(i), 和图标序列前一个点之间直线的斜率)

dp  = [0] * N
for i in range(N):
    cur_k = S + St[i]

    n = len(que)
    l, r = 0, n-1
    pos = -0x7fffffff
    while l <= r:
        mid = l + (r-l) // 2
        if que[mid][2] >= cur_k:
            pos = mid
            r = mid - 1
        else:
            l = mid + 1

    pos = n-1 if pos == -0x7fffffff else pos-1
    selected_k = que[pos][2]

    j = que[pos][0]
    if j == -1:
        dp[i] = St[i]*Sc[i] + S*Sc[N-1]
    else:
        dp[i] = dp[j] - cur_k * Sc[j] + (St[i]*Sc[i] + S*Sc[N-1])

    # 根据凸包下边界性质，比较斜率，更新凸包的下边界
    last_k = 0

    if len(que) > 1:
        while len(que) > 1:
            j = que[-2][0]
            Sc_val = 0 if j == -1 else Sc[j]

            if Sc[i] - Sc_val != 0:
                last_k = (dp[i] - que[-2][1]) / (Sc[i] - Sc_val)
            else:
                if dp[i] - que[-2][1] < 0:
                    last_k = -0x7fffffff
                elif dp[i] - que[-2][1] > 0:
                    last_k = 0x7fffffff
                else:
                    last_k = 0

            if que[-1][2] >= last_k:
                que.pop()
            else:
                break

    j = que[-1][0]
    Sc_val = 0 if j == -1 else Sc[j]

    if Sc[i] - Sc_val != 0:
        last_k = (dp[i] - que[-1][1]) / (Sc[i] - Sc_val)
    else:
        if dp[i] - que[-1][1] < 0:
            last_k = -0x7fffffff
        elif dp[i] - que[-1][1] > 0:
            last_k = 0x7fffffff
        else:
            last_k = 0
    que.append((i, dp[i], last_k))

print(dp[N-1])