n,D = map(int,input().split())
Time = list(map(int,input().split()))

x = Time[0] #買進時間點1的股票的價格
Q = True #有無股票
k=0 #賺

for i in range(1,len(Time)):
    if Q:
        if Time[i] >= x+D:
            k += (Time[i]-x)
            x = Time[i]
            Q = False

    elif not Q:
        if Time[i] <= x-D:
            Q = True
            x = Time[i]

print(k)