from operator import itemgetter
from itertools import *
from bisect import *
from collections import *
from heapq import *
import sys

sys.setrecursionlimit(10 ** 6)

def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def SI(): return sys.stdin.readline()[:-1]
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
int1 = lambda x: int(x) - 1
def MI1(): return map(int1, sys.stdin.readline().split())
def LI1(): return list(map(int1, sys.stdin.readline().split()))
p2D = lambda x: print(*x, sep="\n")
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

def main():
    n,p=MI()
    hh=LI()
    dpf=[0]*n
    dpb=[p]*n
    for i in range(1,n):
        warp=min(dpf[i-1],dpb[i-1])+p
        dpf[i]=min(warp,dpf[i-1]+max(0,hh[i]-hh[i-1]))
        dpb[i]=min(warp,dpb[i-1]+max(0,-hh[i]+hh[i-1]))
    print(min(dpf[-1],dpb[-1]))

main()