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#include <bits/stdc++.h>

using namespace std;

#define int long long

int32_t main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int n,k;
    cin>>n>>k;

    vector<int>nums;

    

    for(int i =0;i<n;i++){
        int a;
        cin>>a;

        nums.push_back(a);
    }
    if(n==1){
        cout<<0<<endl;
        return 0;
    }


    int res = 0;
    int ind_l = -1;
    vector<bool>ify(n,false);
    while(true){
        pair<int,int>mks={0,-1};
        for(int i = 0;i<n;i++){
            if(ify[i]==false){
                mks = max(mks,{nums[i],i});
            }
            
        }
        if(mks.second==-1){
            break;
        }
        ify[mks.second]=true;
        int mn = mks.first;

        if(mks.second == 0){
            if(nums[1]+k<mn){
                res+=(nums[0]-k-nums[1]);
                nums[1] = nums[0]-k;
            }
        }else if(mks.second == n-1){
            if(nums[n-2]+k<mn){
                res+=(nums[n-1]-k-nums[n-2]);
                nums[n-2] = nums[n-1]-k;
            }
        }else{
            if(nums[mks.second+1]+k<mn){
                res+=(nums[mks.second]-k-nums[mks.second+1]);
                nums[mks.second+1] = nums[mks.second]-k;
            }
            if(nums[mks.second-1]+k<mn){
                res+=(nums[mks.second]-k-nums[mks.second-1]);
                nums[mks.second-1] = nums[mks.second]-k;
            }

        }
    }

    cout<<res<<endl;



    return 0;
}