import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = (1 << 63)-1
inf = (1 << 31)-1
# md = 10**9+7
md = 998244353

n, m = LI()
ab = LLI(n)
cs = [0]
for a, b in ab:
    cs.append(cs[-1]+max(a*m, a*(m-1)+b))

s = 0
mn = 0
ans = cs[-1]
for i in range(n)[::-1]:
    a, b = ab[i]
    s += max(a, b)
    mn = min(mn, s)
    cur = cs[i]+s-mn
    if cur > ans: ans = cur

print(ans)