A.cpp

#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; ++i)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; --i)
#define REP(i,a) for(int i=0,_a=(a); i < _a; ++i)

#define DEBUG(X) { cout << #X << " = " << X << endl; }
#define PR(A,n)  { cout << #A << " = "; FOR(_,1,n) cout << A[_] << ' '; cout << endl; }
#define PR0(A,n) { cout << #A << " = "; REP(_,n) cout << A[_] << ' '; cout << endl; }

#define sqr(x) ((x) * (x))
#define ll long long
#define SZ(x) ((int) (x).size())
using namespace std;

int n;
ll d, a[2011];

int main() {
    ios :: sync_with_stdio(0); cin.tie(0);
    while (cin >> n >> d) {
        ll res = 0;
        FOR(i,1,n) {
            cin >> a[i];
            if (i > 1 && a[i] <= a[i-1]) {
                ll need = a[i-1] + 1 - a[i];
                ll add = need / d;
                while (d * add < need) ++add;
                res += add;
                a[i] += add * d;
            }
        }
        cout << res << endl;
    }
}