A. Increasing Sequence

A. Increasing Sequence

time limit per test

1 second

memory limit per test

64 megabytes

input

standard input

output

standard output

A sequence a0,?a1,?...,?at?-?1 is called increasing if ai?-?1?<?ai for each i:?0?<?i?<?t.

You are given a sequence b0,?b1,?...,?bn?-?1 and a positive integer d. In each move you may choose one element of the given sequence and add d to it. What is the least number of moves required to make the given sequence increasing?

Input

The first line of the input contains two integer numbers n and d (2?≤?n?≤?2000,?1?≤?d?≤?106). The second line contains space separated sequence b0,?b1,?...,?bn?-?1 (1?≤?bi?≤?106).

Output

Output the minimal number of moves needed to make the sequence increasing.

Sample test(s)

input

4 2
1 3 3 2

output

3

/* ***********************************************
Author        :
Created Time  :2015/6/2 16:01:09
File Name     :2.cpp
************************************************ */
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <iomanip>
#include <list>
#include <deque>
#include <stack>
#define ull unsigned long long
#define ll long long
#define mod 90001
#define INF 1<<30
#define maxn 10000+10
#define cle(a) memset(a,0,sizeof(a))
const ull inf = 1LL << 61;
const double eps=1e-5;
using namespace std;

bool cmp(int a,int b){
    return a>b;
}

int main()
{
    #ifndef ONLINE_JUDGE
    //freopen("in.txt","r",stdin);
    #endif
    //freopen("out.txt","w",stdout);
	int n,d;
	while(cin>>n>>d){
		int a,b=-INF;
		int ans=0;
		for(int i=1;i<=n;i++){
			cin>>a;
			if(a<=b){
				int x=(b-a)/d+1;
				//if((b-a)%d==0) x++;
				ans+=x;
				a+=x*d;
			}
			b=a;
		}
		cout<<ans<<endl;
	}
    return 0;
}
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