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#ifndef UNCLE
 #pragma GCC optimize("O3,unroll-loops")
#endif

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

#define FOR(i,p,q) for(int i=(p); i<=(q); ++i)
#define ROF(i,p,q) for(int i=(p); i>=(q); --i)
#define REP(i,q) for(int i=0; i<(q); ++i)
#define pb push_back
#define as assign
#define rz resize
#define Co const
#define al(X) X.begin(), X.end()
#define ral(X) X.rbegin(), X.rend()
#define sz(X) (int)((X).size())
#define ckmx(a,b) a=max(a,b)
#define ckmn(a,b) a=min(a,b)
#define V vector
typedef long long ll;
typedef long double ld;
typedef mt19937_64 mt;
#ifndef UNCLE
 typedef basic_string<bool> vb;
 typedef basic_string<int> vi;
 typedef basic_string<ll> vl;
#else
 typedef V<bool> vb;
 typedef V<int> vi;
 typedef V<ll> vl;
#endif

constexpr ll INFl=(ll)1e18+14;
constexpr int INFi=1e9+14, MX_N=5e5+14;

int N,M,Q,K;
void Inpt(){
    cin>>N>>K;
    vi s(N,-1);
    for(int &vv:s) cin>>vv;
    int rs=0;
    REP(_,N){ //potrafię zrobić w O(N) lmao
        FOR(i,1,N-1){
            if(s[i-1]<s[i]-K){
                rs+=(s[i]-s[i-1]-K), s[i-1]=s[i]-K;
            }else if(s[i-1]-s[i]>K) rs+=(s[i-1]-s[i]-K), s[i]=s[i-1]-K;
        }
    }
    cout<<rs<<"\n";
    // vi pr(N,-1);
    // REP(i,N) pr[i]=i;
    // sort(al(pr),[&](Co int a,Co int b){return s[a]<s[b];});
}
signed main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    Inpt();
}