#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int n, k, a[1000], diff;
ll ans = 0;

int main() {
    scanf("%d %d", &n, &k);
    for(int i = 0; i < n; ++i) scanf("%d", &a[i]);
    for(int i = 1; i < n; ++i) {
        diff = abs(a[i] - a[i - 1]);
        if(diff <= k) continue;
        if(a[i] < a[i - 1]){ 
            ans += diff - k;
            a[i] = a[i - 1] - k;
        } else {
            for(int j = i - 1; j >= 0; --j) {
                if(abs(a[j] - a[j + 1]) > k) {
                    ans += abs(a[j] - a[j + 1]) - k;
                    a[j] = a[j + 1] - k;
                } else {
                    break;
                }
            }
        }
    }
    printf("%lld\n", ans);
}