1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
typedef long long ll;
using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

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

	int n, k;
	cin >> n >> k;
	vector<ll> a(n);
	for(int i=0; i<n; ++i) cin >> a[i];
	auto start = a;
	auto wyrownaj = [&](int i) {
		if(a[i-1] >= a[i]) {
			a[i] = max(a[i], a[i-1]-k);
		} else {
			a[i-1] = max(a[i-1], a[i]-k);
		}
	};
	for(int i=1; i<n; ++i) {
		for(int j=i; j>0; --j) wyrownaj(j);
	}
	ll res = 0;
	for(int i=0; i<n; ++i) res += a[i] - start[i];
	cout << res << "\n";

	return 0;
}