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#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#define v vector
#define pb  push_back
#define FF first
#define SS second
#define ALL(a) a.begin(), a.end()

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);
    ll ile, roz;
    cin>>ile>>roz;
    v<ll>aa(ile);
    ll ans = 0;
    for(ll i=0;i<ile;i++){
        cin>>aa[i];
    }
    for(ll i=1;i<ile;i++){
        if(aa[i-1] - roz > aa[i]){
            ans += aa[i-1] - roz - aa[i];
            aa[i] = aa[i-1] - roz;
        }
    }
    for(ll i=ile-1;i>0;i--){
        if(aa[i] - roz > aa[i-1]){
            ans += aa[i] - roz - aa[i-1];
            aa[i-1] = aa[i] - roz;
        }
    }
    cout<<ans;
}