import sys
input = sys.stdin.readline

N,P=map(int,input().split())
A=list(map(int,input().split()))

USE=[0]*N
for i in range(1,N-1):
    if A[i-1]<=A[i]<=A[i+1]:
        USE[i]=1
    if A[i-1]>=A[i]>=A[i+1]:
        USE[i]=1

B=[]
for i in range(N):
    if USE[i]==0:
        B.append(A[i])

if len(B)>=2 and B[0]>=B[1]:
    B.pop(0)

ANS=0

for i in range(0,len(B),2):
    ANS+=min(B[i+1]-B[i],P)

print(ANS)