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// Source: https://usaco.guide/general/io

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

vector<long long> dane;

long long res = 0;
long long k;

void ogarnij(int l, int r){
    long long max_id = -1, maxx = 0;
    if(l > r || l < 0) return;
    for(int i = l; i <= r; i++){
        if(dane[i] >= maxx){
            maxx = dane[i];
            max_id = i;
        }
    }
    if(max_id > l){
        if(maxx - dane[max_id - 1] > k){
            res += maxx - k - dane[max_id - 1];
            dane[max_id - 1] = maxx - k;
        }
    }
    if(max_id < r){
        if(maxx - dane[max_id + 1] > k){
            res += maxx - k - dane[max_id + 1];
            dane[max_id + 1] = maxx - k;
        }
    }
    ogarnij(l, max_id - 1);
    ogarnij(max_id + 1, r);
}
int main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int n; cin >> n >> k;
    dane.resize(n);
    for(int i = 0; i < n; i++) cin >> dane[i];
    ogarnij(0, n - 1);
    cout << res;
}