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#include <bits/stdc++.h>
#define ll long long
#define llu long long unsigned
#define ld long double
#define fr(i,n) for(int i=0;i<n;i++)
#define watch(x) cout<<(#x)<<"=="<<(x)<<endl
#define ft first
#define sc second
#define mp make_pair
#define pb push_back
#define vi vector<int>
#define pii pair<int,int>
#define P 1000000007llu
#define N 500005
#define LC 262144
using namespace std;

int getchar_pos_int() {
    int n=0, c=getchar();
    while('0'<=c&&c<='9') {n=n*10+c-'0'; c=getchar();}
    return n;
}

int n,k,a[N],mx=0,imx,res=0;

int main() {
    n=getchar_pos_int(), k=getchar_pos_int();
    fr(i,n) {
        a[i]=getchar_pos_int();
        if (a[i]>mx) mx=a[i], imx=i;
    }
    if (imx!=n-1) {
        for (int i=imx+1;i<n;i++) {
            if (a[i]<a[i-1]-k) res+=a[i-1]-k-a[i],a[i]=a[i-1]-k;
            else if (a[i]-k>a[i-1]) res+=a[i]-k-a[i-1],a[i-1]=a[i]-k;
           // printf("i=%d res=%d\n",i,res);
        }
    }
    if (imx!=0) {
        for (int i=imx-1;i>=0;i--) {
            if (a[i]<a[i+1]-k) res+=a[i+1]-k-a[i],a[i]=a[i+1]-k;
            else if (a[i]-k>a[i+1]) res+=a[i]-k-a[i+1],a[i+1]=a[i]-k;
        }
    }
    printf("%d\n",res);
}

/*
4 3
3 1 1 1
4 0 0 2 0
2 3 3*/