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

#ifdef DEBUG
auto &operator<<(auto &o, pair<auto, auto> p) {
    return o << "(" << p.first << ", " << p.second <<")";
}
auto operator<<(auto &o, auto x)-> decltype(x.end(), o) {
    o << "{";int i = 0;
    for(auto e : x) o << ", "+!i++<<e;
    return o <<"}";
}
#define debug(x...) cerr << "["#x"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(x)
#else
#define debug(...) {}
#endif

#define int long long
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define pb push_back
#define fi first
#define se second
typedef pair <int, int> pii;


void test() {
    debug("TC______________________");
    int n, k; cin>>n>>k;
    vector <int> v(n);
    vector <int> order(n);

    for (int i=0; i<n; ++i) {
        cin>>v[i];
    } 
    
    v.push_back(-1);
    int ret = 0;
    vector <int> used(n);

    for (int i=0; i<n; ++i) {
        int pos = n;
        for (int j=0; j<n; ++j) {
            if (!used[j] && v[pos] < v[j]) {
                pos = j;
            }
        }

        used[pos] = true;

        debug(pos);
        if (pos > 0) {
            debug(pos-1, pos);

            int add = max(0ll, v[pos] - k - v[pos-1]);
            
            ret += add;
            v[pos-1] += add;
        }
        if (pos + 1 < n) {
            int add = max(0ll, v[pos] - k - v[pos+1]);
        
            ret += add;
            v[pos+1] += add;
        }
        debug(v, ret);
    }

    cout<<ret<<'\n';

}

signed main() {
  ios_base::sync_with_stdio(0); cin.tie(0);
  int t = 1;
  while (t--) {
    test();
  }
}