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#include <bits/stdc++.h>
using namespace std;

#define f first
#define s second
typedef long long ll;
const ll M = 1000LL*1000LL*1000LL+7LL;

void make_close(int l, int r, int k, vector<int>& f, int& res){
    if( f[l] + k < f[r] ){
        res += (f[r] - f[l] - k);
        f[l] = f[r] - k;
    }
    if( f[r] + k < f[l] ){
        res += (f[l] - f[r] - k);
        f[r] = f[l] - k;
    }
}

void solve(){
    int n, k; int res = 0;
    cin >> n >> k;
    vector<int>fragments(n, 0);
    for(int i = 0; i < n; i++) cin >> fragments[i];
    for(int i = 1; i < n; i++){
        int j = i-1;
        while( j>=0 && abs(fragments[j]-fragments[j+1]) > k ){
            make_close(j, j+1, k, fragments, res);
            j--;
        }
    }
    cout << res << "\n";
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    solve();
}